TY - GEN
A1 - Bubeck, Christoph
A1 - Laschewsky, André
A1 - Lupo, Donald
A1 - Neher, Dieter
A1 - Ottenbreit, Petra
A1 - Paulus, Wolfgang
A1 - Prass, Werner
A1 - Ringsdorf, Helmut
A1 - Wegner, Gerhard
T1 - Amphiphilic dyes for nonlinear optics: Dependence of second harmonic generation on functional group substitution
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 082
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17201
ER -
TY - GEN
A1 - Schmälzlin, Elmar
A1 - Dongen, Joost T. van
A1 - Klimant, Ingo
A1 - Marmodée, Bettina
A1 - Steup, Martin
A1 - Fishahn, Joachim
A1 - Geigenberger, Peter
A1 - Löhmannsröben, Hans-Gerd
T1 - An optical multifrequency phase-modulation method using microbeads for measuring intracellular oxygen concentrations in plants
N2 - A technique has been developed to measure absolute intracellular oxygen concentrations in green plants. Oxygen-sensitive phosphorescent microbeads were injected into the cells and an optical multifrequency phase-modulation technique was used to discriminate the sensor signal from the strong autofluorescence of the plant tissue. The method was established using photosynthesis-competent cells of the giant algae Chara corallina L., and was validated by application to various cell types of other plant species.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 007
Y1 - 2005
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12232
ER -
TY - THES
A1 - Kröner, Dominik
T1 - Analysis and control of light-induced processes in molecules: Electron and nuclear quantum dynamics for aspects of stereoisomerism and spectroscopy
T1 - Analyse und Kontrolle lichtinduzierter Prozesse in Molekülen: Elektronen- und Kernquantendynamik für Aspekte der Stereoisomerie und Spektroskopie
N2 - The habilitation thesis covers theoretical investigations on light-induced processes in molecules. The study is focussed on changes of the molecular electronic structure and geometry, caused either by photoexcitation in the event of a spectroscopic analysis, or by a selective control with shaped laser pulses. The applied and developed methods are predominantly based on quantum chemistry as well as on electron and nuclear quantum dynamics, and in parts on molecular dynamics. The studied scientific problems deal with stereoisomerism and the question of how to either switch or distinguish chiral molecules using laser pulses, and with the essentials for the simulation of the spectroscopic response of biochromophores, in order to unravel their photophysics. The accomplished findings not only explain experimental results and extend existing approaches, but also contribute significantly to the basic understanding of the investigated light-driven molecular processes. The main achievements can be divided in three parts: First, a quantum theory for an enantio- and diastereoselective or, in general, stereoselective laser pulse control was developed and successfully applied to influence the chirality of molecular switches. The proposed axially chiral molecules possess different numbers of "switchable" stable chiral conformations, with one particular switch featuring even a true achiral "off"-state which allows to enantioselectively "turn on" its chirality. Furthermore, surface mounted chiral molecular switches with several well-defined orientations were treated, where a newly devised highly flexible stochastic pulse optimization technique provides high stereoselectivity and efficiency at the same time, even for coupled chirality-changing degrees of freedom. Despite the model character of these studies, the proposed types of chiral molecular switches and, all the more, the developed basic concepts are generally applicable to design laser pulse controlled catalysts for asymmetric synthesis, or to achieve selective changes in the chirality of liquid crystals or in chiroptical nanodevices, implementable in information processing or as data storage. Second, laser-driven electron wavepacket dynamics based on ab initio calculations, namely time-dependent configuration interaction, was extended by the explicit inclusion of magnetic field-magnetic dipole interactions for the simulation of the qualitative and quantitative distinction of enantiomers in mass spectrometry by means of circularly polarized ultrashort laser pulses. The developed approach not only allows to explain the origin of the experimentally observed influence of the pulse duration on the detected circular dichroism in the ion yield, but also to predict laser pulse parameters for an optimal distinction of enantiomers by ultrashort shaped laser pulses. Moreover, these investigations in combination with the previous ones provide a fundamental understanding of the relevance of electric and magnetic interactions between linearly or non-linearly polarized laser pulses and (pro-)chiral molecules for either control by enantioselective excitation or distinction by enantiospecific excitation. Third, for selected light-sensitive biological systems of central importance, like e.g. antenna complexes of photosynthesis, simulations of processes which take place during and after photoexcitation of their chromophores were performed, in order to explain experimental (spectroscopic) findings as well as to understand the underlying photophysical and photochemical principles. In particular, aspects of normal mode mixing due to geometrical changes upon photoexcitation and their impact on (time-dependent) vibronic and resonance Raman spectra, as well as on intramolecular energy redistribution were addressed. In order to explain unresolved experimental findings, a simulation program for the calculation of vibronic and resonance Raman spectra, accounting for changes in both vibrational frequencies and normal modes, was created based on a time-dependent formalism. In addition, the influence of the biochemical environment on the electronic structure of the chromophores was studied by electrostatic interactions and mechanical embedding using hybrid quantum-classical methods. Environmental effects were found to be of importance, in particular, for the excitonic coupling of chromophores in light-harvesting complex II. Although the simulations for such highly complex systems are still restricted by various approximations, the improved approaches and obtained results have proven to be important contributions for a better understanding of light-induced processes in biosystems which also adds to efforts of their artificial reproduction.
N2 - Die Habilitationsschrift behandelt theoretische Untersuchungen von durch Licht ausgelösten Prozessen in Molekülen. Der Schwerpunkt liegt dabei auf Veränderungen in der Elektronenstruktur und der Geometrie der Moleküle, die durch Bestrahlung mit Licht entweder bei einer spektroskopischen Untersuchung oder bei gezielter Kontrolle durch geformte Laserpulse herbeigeführt werden. Um die dabei auftretende Elektronen- und Kerndynamik zu simulieren, wurden vornehmlich quantentheoretische Methoden eingesetzt und weiterentwickelt. Die wissenschaftlichen Fragestellungen beschäftigen sich mit dem gezielten Verändern und dem Erkennen der räumlichen Struktur von Molekülen ohne Drehspiegelachse, der sog. molekularen Chiralität, sowie mit durch Licht eingeleiteten Prozessen in biologisch relevanten Pigmenten auf sehr kurzen Zeitskalen. Die entwickelten Ansätze und gewonnenen Erkenntnisse lassen sich drei Haupterfolge unterteilen: Erstens gelang die Entwicklung einer generellen Kontrolltheorie für das Ein- und Umschalten von molekularer Chiralität mit geformten Laserpulsen. Dabei wird die räumliche Struktur der vorgeschlagenen molekularen Schalter zwischen ihren stabilen sog. stereoisomeren Formen selektiv geändert, was sich auf ihre optischen und chemischen Eigenschaften auswirkt. Für komplexere Bedingungen, wie z.B. auf einer Oberfläche verankerten molekularen Schaltern verschiedener Orientierung, wurde eine neue Pulsoptimierungsmethode basierend auf Wahrscheinlichkeiten und Statistik entwickelt. Solche laserpulskontrollierten chiralen molekularen Schalter hofft man u.a. in der Nanotechnologie zum Einsatz zu bringen, wo sie z.B. als Informationsspeicher dienen könnten. Zweitens konnte geklärt werden, welche die wesentlichen Einflüsse sind, die das Erkennen von sog. Enantiomeren, das sind spiegelbildliche Moleküle von entgegengesetzter Chiralität, nach Ionisierung durch ultrakurze zirkular polarisierte Laserpulse ermöglichen. Diese Form des sog. Zirkulardichroismus in der Ionenausbeute erlaubt die quantitative und qualitative Unterscheidung von Enantiomeren in der Massenspektrometrie. Durch Simulation der Elektronendynamik während der Laseranregung konnte u.a. erstmals gezeigt werden, dass neben der Zirkularpolarisation der Laserpulse vor allem die schwachen magnetischen Wechselwirkungen für die Unterscheidung entscheidend sind. Drittens wurden die Spektren von in der Natur vorkommenden Pigmenten simuliert, welche u.a. an wichtigen biologischen Funktionen, wie dem Sammeln von Sonnenenergie für die Photosynthese, beteiligt sind. Die Lichtanregung führt dabei zu einer Veränderung der Elektronenstruktur und Geometrie der Pigmente, wobei letzteres wichtige Konsequenzen für die Verteilung der Energie auf die spektroskopisch beobachteten Molekülschwingungen mit sich bringen. Auch der wichtige Einfluss der biochemischen Umgebung auf die Elektronenstruktur der Pigmente bzw. den Energietransfer zwischen solchen wurde untersucht. Neben der Klärung experimenteller Ergebnisse ermöglichen die Untersuchungen neue Einblicke in die fundamentalen Prozesse kurz nach der Lichtanregung -- Erkenntnisse, die auch für die technische Nachahmung der biologischen Funktionen von Bedeutung sein können.
KW - Elektronendynamik
KW - chirale Schalter
KW - chirale Erkennung
KW - Biochromophore
KW - Laserpulskontrolle
KW - electron dynamics
KW - chiral switches
KW - chiral recognition
KW - biochromophores
KW - laser pulse control
Y1 - 2013
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-70477
ER -
TY - GEN
A1 - Billard, Isabelle
A1 - Ansoborlo, Eric
A1 - Apperson, Kathleen
A1 - Arpigny, Sylvie
A1 - Azenha, M. Emilia
A1 - Birch, David
A1 - Bros, Pascal
A1 - Burrows, Hugh D.
A1 - Choppin, Gregory
A1 - Kumke, Michael Uwe
T1 - Aqueous solutions of Uranium(VI) as studied by time-resolved emission spectroscopy : a Round-Robin Test
N2 - Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO22+aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 005
KW - uranium (VI)
KW - intercomparison
KW - speciation
Y1 - 2003
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12318
ER -
TY - GEN
A1 - Kort, C. A. D. de
A1 - Peter, Martin G.
A1 - Koopmanschap, A. B.
T1 - Binding and degradation of juvenile hormone III by haemolymph proteins of the Colorado potato beetle: a re-examination
N2 - The haemolymph of the adult Colorado potato beetle, Lepinotarsa decemlineata Say, contains a high molecular weight (MW > 200,000) JH-III specific binding protein. The Kd value of the protein for racemic JH-III is 1.3 ± 0.2 × 10−7 M. It has a lower affinity for racemic JH-I and it does not bind JH-III-diol or JH-III-acid. The binding protein does discriminate between the enantiomers of synthetic, racemic JH-III as was determined by stereochemical anaysis of the bound and the free JH-III. Incubation of racemic JH-III with crude haemolymph results in preferential formation of (10S)-JH-III-acid, the unnatural configuration. The JH-esterase present in L. decemlineata haemolymph is not enantioselective. It is concluded that the most important function of the binding protein is that of a specific carrier, protecting the natural hormone against degradation by esterases. The carrier does not protect JH-I as efficiently as the lower homologue.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 068
KW - Juvenile hormone
KW - Leptinotarsa decemlineata
KW - JH-III-specific carrier protein
KW - enantioselectivity
Y1 - 1983
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-16777
ER -
TY - GEN
A1 - Peter, Martin G.
A1 - Andersen, Svend Olav
A1 - Hartmann, Rudolf
A1 - Miessner, Merle
A1 - Roepstorff, Peter
T1 - Catecholamine-protein conjugates : isolation of 4-phenylphenoxazin-2-ones from oxidative coupling of N-acetyldopamine with alipathic amino acids
N2 - 4-Phenylphenoxazinones were isolated after biomimetic oxidation, using diphenoloxidases of insect cuticle, mushroom tyrosinase, or after autoxidation of N-acetyldopamine (Image ) in the presence of β-alanine, β-alanine methyl ester or N-acetyl-L-lysine. They are formed presumably by addition of 2-aminoalkyl-5-alkylphenols to the o-quinone of biphenyltetrol which, in turn, arises from oxidative coupling of. The structures of present the first examples for the assembly of reasonably stable intermediates in the rather complex process of chemical modifications of aliphatic amino acid residues by o-quinones.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 062
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17571
ER -
TY - THES
A1 - Glatzel, Stefan
T1 - Cellulose based transition metal nano-composites : structuring and development
T1 - Zellulose-basierte Übergangsmetall Nano-Komposite : Strukturierung und Entwicklung
N2 - Cellulose is the most abundant biopolymer on earth. In this work it has been used, in various forms ranging from wood to fully processed laboratory grade microcrystalline cellulose, to synthesise a variety of metal and metal carbide nanoparticles and to establish structuring and patterning methodologies that produce highly functional nano-hybrids. To achieve this, the mechanisms governing the catalytic processes that bring about graphitised carbons in the presence of iron have been investigated. It was found that, when infusing cellulose with an aqueous iron salt solution and heating this mixture under inert atmosphere to 640 °C and above, a liquid eutectic mixture of iron and carbon with an atom ratio of approximately 1:1 forms. The eutectic droplets were monitored with in-situ TEM at the reaction temperature where they could be seen dissolving amorphous carbon and leaving behind a trail of graphitised carbon sheets and subsequently iron carbide nanoparticles. These transformations turned ordinary cellulose into a conductive and porous matrix that is well suited for catalytic applications. Despite these significant changes on the nanometre scale the shape of the matrix as a whole was retained with remarkable precision. This was exemplified by folding a sheet of cellulose paper into origami cranes and converting them via the temperature treatment in to magnetic facsimiles of those cranes. The study showed that the catalytic mechanisms derived from controlled systems and described in the literature can be transferred to synthetic concepts beyond the lab without loss of generality. Once the processes determining the transformation of cellulose into functional materials were understood, the concept could be extended to other metals and metal-combinations. Firstly, the procedure was utilised to produce different ternary iron carbides in the form of MxFeyC (M = W, Mn). None of those ternary carbides have thus far been produced in a nanoparticle form. The next part of this work encompassed combinations of iron with cobalt, nickel, palladium and copper. All of those metals were also probed alone in combination with cellulose. This produced elemental metal and metal alloy particles of low polydispersity and high stability. Both features are something that is typically not associated with high temperature syntheses and enables to connect the good size control with a scalable process. Each of the probed reactions resulted in phase pure, single crystalline, stable materials. After showing that cellulose is a good stabilising and separating agent for all the investigated types of nanoparticles, the focus of the work at hand is shifted towards probing the limits of the structuring and pattering capabilities of cellulose. Moreover possible post-processing techniques to further broaden the applicability of the materials are evaluated. This showed that, by choosing an appropriate paper, products ranging from stiff, self-sustaining monoliths to ultra-thin and very flexible cloths can be obtained after high temperature treatment. Furthermore cellulose has been demonstrated to be a very good substrate for many structuring and patterning techniques from origami folding to ink-jet printing. The thereby resulting products have been employed as electrodes, which was exemplified by electrodepositing copper onto them. Via ink-jet printing they have additionally been patterned and the resulting electrodes have also been post functionalised by electro-deposition of copper onto the graphitised (printed) parts of the samples. Lastly in a preliminary test the possibility of printing several metals simultaneously and thereby producing finely tuneable gradients from one metal to another have successfully been made. Starting from these concepts future experiments were outlined. The last chapter of this thesis concerned itself with alternative synthesis methods of the iron-carbon composite, thereby testing the robustness of the devolved reactions. By performing the synthesis with partly dissolved scrap metal and pieces of raw, dry wood, some progress for further use of the general synthesis technique were made. For example by using wood instead of processed cellulose all the established shaping techniques available for wooden objects, such as CNC milling or 3D prototyping, become accessible for the synthesis path. Also by using wood its intrinsic well defined porosity and the fact that large monoliths are obtained help expanding the prospect of using the composite. It was also demonstrated in this chapter that the resulting material can be applied for the environmentally important issue of waste water cleansing. Additionally to being made from renewable resources and by a cheap and easy one-pot synthesis, the material is recyclable, since the pollutants can be recovered by washing with ethanol. Most importantly this chapter covered experiments where the reaction was performed in a crude, home-built glass vessel, fuelled – with the help of a Fresnel lens – only by direct concentrated sunlight irradiation. This concept carries the thus far presented synthetic procedures from being common laboratory syntheses to a real world application. Based on cellulose, transition metals and simple equipment, this work enabled the easy one-pot synthesis of nano-ceramic and metal nanoparticle composites otherwise not readily accessible. Furthermore were structuring and patterning techniques and synthesis routes involving only renewable resources and environmentally benign procedures established here. Thereby it has laid the foundation for a multitude of applications and pointed towards several future projects reaching from fundamental research, to application focussed research and even and industry relevant engineering project was envisioned.
N2 - Die vorliegende Arbeit beschäftigt sich mit der Synthese und Strukturierung von Nanokompositen, d.h. mit ausgedehnten Strukturen, welche Nanopartikel enthalten. Im Zuge der Arbeit wurde der Mechanismus der katalytischen Graphitisierung, ein Prozess, bei dem ungeordneter Kohlenstoff durch metallische Nanopartikel in geordneten (graphitischen) Kohlenstoff überführt wird, aufgeklärt. Dies wurde exemplarisch am Beispiel von Zellulose und Eisen durchgeführt. Die untersuchte Synthese erfolgte durch das Lösen eines Eisensalzes in Wasser und die anschließende Zugabe von so viel Zellulose, dass das die gesamte Eisensalzlösung aufgenommen wurde. Die so erhaltene Mischung wurde anschließend unter Schutzgas innerhalb kürzester Zeit auf 800 °C erhitzt. Hierbei zeigte sich, dass zu Beginn der Reaktion Eisenoxidnanopartikel (Rost) auf der Oberfläche der Zellulose entstehen. Beim weiteren Erhöhen der Temperatur werden diese Partikel zu Eisenpartikeln umgewandelt. Diese lösen dann kleine Bereiche der Zellulose auf, wandeln sich in Eisenkarbid um und scheiden graphitischen Kohlenstoff ab. Nach der Reaktion sind die Zellulosefasern porös, jedoch bleibt ihre Faserstruktur vollkommen erhalten. Dies konnte am Beispiel eines Origamikranichs gezeigt werden, welcher nach dem Erhitzen zwar seine Farbe von Weiß zu Schwarz verändert hatte, ansonsten aber seine Form vollkommen beibehält. Aufgrund der eingebetteten Eisenkarbid Nanopartikel war der Kranich außerdem hochgradig magnetisch. Basierend auf dieser Technik wurden außerdem winzige metallische Nanopartikel aus Nickel, Nickel-Palladium, Nickel-Eisen, Kobalt, Kobalt-Eisen und Kupfer, sowie Partikel aus den Verbundkarbiden Eisen-Mangan-Karbid und Eisen-Wolfram-Karbid, jeweils in verschiedenen Mischungsverhältnissen, hergestellt und analysiert. Da die Vorstufe der Reaktion flüssig ist, konnte diese mit Hilfe eines einfachen kommerziellen Tintenstrahldruckers strukturiert auf Zellulosepapier aufgebracht werden. Dies ermöglicht gezielt Leiterbahnen, bestehend aus graphitisiertem Kohlenstoff, in ansonsten ungeordnetem (amorphen) Kohlenstoff zu erzeugen. Diese Methode wurde anschließend auf Systeme mit mehreren Metallen übertragen. Hierbei wurde die Tatsache, dass moderne Drucker vier Tintenpatronen beherbergen, ausgenutzt um Nanopartikel mit beliebigen Mischungsverhältnisse von Metallen zu erzeugen. Dieser Ansatz hat potentiell weitreichende Auswirkungen im Feld der Katalyse, da hiermit hunderte oder gar tausende Mischungen simultan erzeugt und getestet werden können. Daraus würden sich große Zeiteinsparungen (Tage anstelle von Monaten) bei der Entwicklung neuer Katalysatoren ergeben. Der letzte Teil der Arbeit beschäftigt sich mit der umweltfreundlichen Synthese der obengenannten Komposite. Hierbei wurden erfolgreich Altmetall und Holzstücke als Ausgangstoffe verwandt. Zusätzlich wurde gezeigt, dass die gesamte Synthese ohne Verwendung von hochentwickeltem Equipment durchgeführt werden kann. Dazu wurde eine sogenannte Fresnel-Linse genutzt um Sonnenlicht zu bündeln und damit direkt die Reaktionsmischung auf die benötigten 800 °C zu erhitzen. Weiterhin wurde ein selbst gebauter Glasreaktor eingesetzt und gezeigt, wie das entstehende Produkt als Abwasserfilter genutzt werden kann. Die Kombination dieser Ergebnisse bedeutet, dass dieses System sich beispielsweise zum Einsatz in Katastrophenregionen eignen würde, um ohne Strom und besondere Ausrüstung vor Ort Wasserfilter herzustellen.
KW - Zellulose
KW - Übergangsmetalle
KW - Carbide
KW - Nanopartikel
KW - Komposite
KW - Cellulose
KW - Transitionmetals
KW - Carbides
KW - Nanoparticles
KW - Composites
Y1 - 2013
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-64678
ER -
TY - GEN
A1 - Schäfer-Bung, Boris
A1 - Nest, Mathias
T1 - Correlated dynamics of electrons with reduced two-electron density matrices
N2 - We present an approach to the correlated dynamics of many-electron systems. We show, that the twoelectron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 100
Y1 - 2008
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41774
SN - 1866-8372
ER -
TY - GEN
A1 - Andersen, Svend Olav
A1 - Perter, Martin G.
A1 - Roepstorff, Peter
T1 - Cuticle-catalyzed coupling between N-acetylhistidine and N-acetyldopamine
N2 - Several types of insect cuticle contain enzymes catalyzing the formation ofof adducts between N-acetyldopamine (NADA) and N-acetylhistidine (NAH). Two such adducts, NAH-NADA-I and NAH NADA-II, have been isolated and their structures determined. In one of the adducts the link connecting the two residues occurs between the I-position (ß-position) in the NADA side chain and the 1-N atom (τ-N) in the imidazole ring of histidine. Diphenoloxidase activity alone is not sufficient for formation of this adduct, whereas extracts containing both diphenoloxidase and o-quinone-p-quinone methide isomerase activities catalyze the coupling reaction. The adduct consists of a mixture of two diastereomers and they are presumably formed by spontaneous reaction between enzymatically produced NADA-p-quinone methide and N-acetylhistidine. The other adduct has been identified as a ring addition product of N-acetylhistidine and NADA. In contrast to the former adduct it can be formed by incubation of the two substrates with mushroom tyrosinase alone. An adduct between N-acetylhistidine and the benzodioxan-type NADA-dimer is produced in vitro, when the N-acetylhistidine-NADA adduct is incubated with NADA and locust cuticle containing a 1,2-dehydro-NADA generating enzyme system. Trimeric NADA-polymerization products of the substituted benzodioxan-type have been obtained from in vivo sclerotized locust cuticle, confirming the ability of cuticle to produce NADA-oligomers. The results indicate that some insect cuticles contain enzymes promoting linkage of oxidized NADA to histidine residues. It is suggested that histidine residues in the cuticular proteins can serve as acceptors for oxidized NADA and that further addition of NADA-residues to the phenolic groups of bound NADA can occur, resulting in formation of protein-linked NADA-oligomers. The coupling reactions identified may be an important step in natural cuticular sclerotization.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 072
KW - sclerotization
KW - quinone
KW - quinone methide
KW - o-quinone isomerase
KW - Hyalophora cecropia
KW - Locusta migratoria
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-16762
ER -
TY - THES
A1 - Mondal, Suvendu Sekhar
T1 - Design of isostructural metal-imidazolate frameworks : application for gas storage
T1 - Synthese isostruktureller Metall-Imidazolat Frameworks : Anwendung für Gasspeicherung
N2 - The sharply rising level of atmospheric carbon dioxide resulting from anthropogenic emissions is one of the greatest environmental concerns facing our civilization today. Metal-organic frameworks (MOFs) are a new class of materials that constructed by metal-containing nodes bonded to organic bridging ligands. MOFs could serve as an ideal platform for the development of next generation CO2 capture materials owing to their large capacity for the adsorption of gases and their structural and chemical tunability. The ability to rationally select the framework components is expected to allow the affinity of the internal pore surface toward CO2 to be precisely controlled, facilitating materials properties that are optimized for the specific type of CO2 capture to be performed (post-combustion capture, precombustion capture, or oxy-fuel combustion) and potentially even for the specific power plant in which the capture system is to be installed. For this reason, significant effort has been made in recent years in improving the gas separation performance of MOFs and some studies evaluating the prospects of deploying these materials in real-world CO2 capture systems have begun to emerge. We have developed six new MOFs, denoted as IFPs (IFP-5, -6, -7, -8, -9, -10, IFP = Imidazolate Framework Potsdam) and two hydrogen-bonded molecular building block (MBB, named as 1 and 2 for Zn and Co based, respectively) have been synthesized, characterized and applied for gas storage. The structure of IFP possesses 1D hexagonal channels. Metal centre and the substituent groups of C2 position of the linker protrude into the open channels and determine their accessible diameter. Interestingly, the channel diameters (range : 0.3 to 5.2 Å) for IFP structures are tuned by the metal centre (Zn, Co and Cd) and substituent of C2 position of the imidazolate linker. Moreover hydrogen bonded MBB of 1 and 2 is formed an in situ functionalization of a ligand under solvothermal condition. Two different types of channels are observed for 1 and 2. Materials contain solvent accessible void space. Solvent could be easily removed by under high vacuum. The porous framework has maintained the crystalline integrity even without solvent molecules. N2, H2, CO2 and CH4 gas sorption isotherms were performed. Gas uptake capacities are comparable with other frameworks. Gas uptake capacity is reduced when the channel diameter is narrow. For example, the channel diameter of IFP-5 (channel diameter: 3.8 Å) is slightly lower than that of IFP-1 (channel diameter: 4.2 Å); hence, the gas uptake capacity and Brunauer-Emmett-Teller (BET) surface area are slightly lower than IFP-1. The selectivity does not depend only on the size of the gas components (kinetic diameter: CO2 3.3 Å, N2 3.6 Å and CH4 3.8 ) but also on the polarizability of the surface and of the gas components. IFP-5 and-6 have the potential applications for the separation of CO2 and CH4 from N2-containing gas mixtures and CO2 and CH4 containing gas mixtures. Gas sorption isotherms of IFP-7, -8, -9, -10 exhibited hysteretic behavior due to flexible alkoxy (e.g., methoxy and ethoxy) substituents. Such phenomenon is a kind of gate effects which is rarely observed in microporous MOFs. IFP-7 (Zn-centred) has a flexible methoxy substituent. This is the first example where a flexible methoxy substituent shows the gate opening behavior in a MOF. Presence of methoxy functional group at the hexagonal channels, IFP-7 acted as molecular gate for N2 gas. Due to polar methoxy group and channel walls, wide hysteretic isotherm was observed during gas uptake. The N2 The estimated BET surface area for 1 is 471 m2 g-1 and the Langmuir surface area is 570 m2 g-1. However, such surface area is slightly higher than azolate-based hydrogen-bonded supramolecular assemblies and also comparable and higher than some hydrogen-bonded porous organic molecules.
N2 - Metallorganische Gerüstverbindungen (MOFs) sind eine neue Klasse von porösen Koordinationspolymeren, die aus Metall-Knoten und verbrückenden Liganden bestehen. MOFs können Gasgemische trennen und Gase speichern. Aufgrund ihres modularen Aufbaus können die MOF-Eigenschaften systematisch variiert werden. Ein wichtiges Ziel für das Design von MOFs ist die Synthese von Materialien, die eine hohe selektive Aufnahmefähigkeit und -kapazität für Kohlenstoffdioxid besitzen. Im Rahmen der Arbeit ist es gelungen sechs neue MOFs (IFP-5, -6, -7, -8, -9 und -10) zu synthetisieren. Diese MOFs tragen die Kurzbezeichnung IFP. IFP steht als Abkürzung für Imidazolat-Framework-Potsdam (Imidazolat-basierte Gerüstverbindung Potsdam). In diesen IFPs wurde der Metallknoten (Zink, Cobalt, Cadmium) und der Brückenligand, ein 2-substituiertes Imidazolat-amid-imidat, in der Position variiert, um gute und selektive Sorptionseigenschaften für Kohlenstoffdioxid zu erzielen. Von den synthetisierten Verbindungen hat das IFP-5 die besten Sorptionseigenschaften für Kohlenstoffdioxid. Es konnte weiter gezeigt werden, dass sich die IFP-Struktur bei der Wahl von geeigneten Substituenten 2, wie z.B. Methoxy und Ethoxy auch für das Design von gate-opening (Tür-öffnenden) Effekten eignet. Diese Effekte können wiederum genutzt werden, um selektiv Gasmischungen zu trennen. Wenn man das 4,5-Dicyano-2-methoxy-imidazol in Gegenwart von Zink- und Cobalt-Salzen unter solvothermalen Bedingungen zur Reaktion bringt, erhält man beispiellose supramolekulare Wasserstoffbrückenbindungen zu einem dreidimensionalen Netzwerk, die mit Kanälen verknüpft sind. Diese Kanäle können von Lösungsmittelmolekülen (Wasser und Dimethylformamid) befreit werden und Gase aufnehmen. Insgesamt besteht nun die neue MOF-Klasse der Imidazolat-basierten IFPs aus Vertretern. Das Potential der 2-substituierten 4,5-Dicyanoimidazole ist nicht nur auf die Bildung von porösen Koordinationspolymeren beschränkt, sondern kann auch für die Synthese von bisher unbekannten supramolekularen Strukturen genutzt werden.
KW - Metal-organic framework
KW - Gas Sorption
KW - Cobalt
KW - Zinc
KW - Ionic Liquid
KW - metal-organic framework
KW - gas sorption
KW - cobalt
KW - zinc
KW - ionic liquid
Y1 - 2013
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-69692
ER -
TY - GEN
A1 - Tsukamoto, Junko
A1 - Heabel, Sophie
A1 - Valenca, Gustavo P.
A1 - Peter, Martin
A1 - Franco, Telma
T1 - Enzymatic direct synthesis of acrylic acid esters of mono- and disaccharides
N2 - BACKGROUND: There is an increased need to replace materials derived from fossil sources by renewables. Sugar-cane derived carbohydrates are very abundant in Brazil and are the cheapest sugars available in the market, with more than 400 million tons of sugarcane processed in the year 2007. The objective of this work was to study the preparation of sugar acrylates from free sugars and free acrylic acid, thus avoiding the previous preparation of protected sugar derivatives, such as glycosides, or activated acrylates, such as vinyl acrylate. RESULTS: Lipase catalyzed esterification of three mono- and two disaccharides with acrylic acid, in the presence or absence of molecular sieves was investigated. The reactions were monitored by high-performance liquid chromatography (HPLC) and the products were analyzed by matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry. The main products are mono- and diacrylates, while higher esters are formed as minor products. The highest conversion to sugar acrylates was observed for the D-glucose and D-fructose, followed by D-xylose and D-maltose. Molecular sieves had no pronounced effect on the conversion CONCLUSIONS: A feasible method is described to produce and to characterize sugar acrylates, including those containing more than two acrylate groups. The process for production of these higher esters could potentially be optimized further to produce molecules for cross-linking in acrylate polymerization and other applications. The direct enzymatic esterification of free carbohydrates with acrylic acid is unprecedented.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 106
KW - carbohydrate esters
KW - enzymatic esterification
KW - acrylic acid esters
KW - MALDI-TOF mass spectrometry
Y1 - 2008
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-42652
ER -
TY - GEN
A1 - Oliveira Jr, E. N.
A1 - Gueddari, Nour E. El
A1 - Moerschbacher, Bruno M.
A1 - Peter, Martin
A1 - Franco, Telma
T1 - Growth of phytopathogenic fungi in the presence of partially acetylated chitooligosaccharides
N2 - Four phytopathogenic fungi were cultivated up to six days in media containing chitooligosaccharide mixtures differing in average DP and FA. The three different mixtures were named Q3 (which contained oligosaccharides ofDP2–DP10, withDP2–DP7 asmain components), Q2 (which contained oligosaccharides of DP2–DP12, with DP2–DP10 as main components) and Q1 (which derived from Q2 and contained oligomers of DP5–DP8 with hexamer and a heptamer as the main components). The novel aspect of this work is the description of the effect of mixtures of oligosaccharides with different and known composition on fungal growth rates. The growth rate of Alternaria alternata and Rhizopus stolonifer was initially inhibited by Q3 and Q2 at higher concentrations. Q1 had a growth stimulating effect on these two fungi. Growth of Botrytis cinerea was inhibited by Q3 and Q2, while Q1 had no effect on the growth of this fungus. Growth of Penicillium expansum was only slightly inhibited by higher concentrations of sample Q3, while Q2 and Q1 had no effect. The inhibition of growth rates or their resistance toward chitooligosaccharides correlated with the absence or presence of chitinolytic enzymes in the culture media, respectively.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 105
KW - Chitosan
KW - Chitinase
KW - Fungi
KW - Oligosaccharides
KW - Phytopathogens
Y1 - 2008
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-42646
ER -
TY - GEN
A1 - Köberle, Peter
A1 - Laschewsky, André
T1 - Hybrid materials from organic polymers and inorganic salts
N2 - The prepaparation of amorphous, homogeneous blends of zwitterionic polymers and transition metal salts was investigated. Homogeneous miscibility was achieved in many cases up to equimolar amounts of salt, depending on the anion and cation chosen. Various analytical techniques point to a solid state solution of the inorganic ions in the polymer matrix.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 086
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-26884
ER -
TY - GEN
A1 - Elbert, R.
A1 - Laschewsky, André
A1 - Ringsdorf, H.
T1 - Hydrophilic spacer groups in polymerizable lipids: formation of biomembrane models from bulk polymerized lipids
N2 - A variety of polymerizable lipids containing a hydrophilic spacer group between the reactive group and the main amphiphilic structure have been synthesized. They were investigated in monolayers, liposomes, and multilayers. When the spacer concept was used, efficient decoupling of the motions of the polymeric chain and the amphiphilic side groups is achieved. Thus, the often found loss of the important fluid phases by polymerization is avoided. Polymeric monolayers of the spacer lipid, prepared either by polymerization in the monolayer or by spreading of prepolymerized lipid, exhibit nearly identical surface pressure-area diagrams. Most distinctly, the successful decoupling of the motions of the polymer main chain and the membrane forming amphiphilic side groups is demonstrated by the self-organization of bulk polymerized spacer lipids to polymeric liposomes. In addition, spacer lipids are able to build polymeric Langmuir-Blodgett multilayers. The decoupling of the polymer main chain and the membrane-forming amphiphilic side groups enables the deposition of already polymeric monolayers onto supports to form defined multilayers. If, alternatively, monomeric monolayers are deposited and polymerized on the support, defects in the layers due to structural changes during the polymerization are avoided by the flexible spacer group.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 095
Y1 - 1985
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17361
ER -
TY - GEN
A1 - Niederkrüger, Matthias
A1 - Salb, Christian
A1 - Beck, Michael
A1 - Hildebrandt, Niko
A1 - Löhmannsröben, Hans-Gerd
A1 - Marowsky, Gerd
T1 - Improvement of a fluorescence immunoassay with a compact diode-pumped solid state laser at 315 nm
N2 - We demonstrate the improvement of fluorescence immunoassay (FIA) diagnostics in deploying a newly developed compact diode-pumped solid state (DPSS) laser with emission at 315 nm. The laser is based on the quasi-three-level transition in Nd:YAG at 946 nm. The pulsed operation is either realized by an active Q-switch using an electro-optical device or by introduction of a Cr4+:YAG saturable absorber as passive Q-switch element. By extra-cavity second harmonic generation in different nonlinear crystal media we obtained blue light at 473 nm. Subsequent mixing of the fundamental and the second harmonic in a β-barium-borate crystal provided pulsed emission at 315 nm with up to 20 μJ maximum pulse energy and 17 ns pulse duration. Substitution of a nitrogen laser in a FIA diagnostics system by the DPSS laser succeeded in considerable improvement of the detection limit. Despite significantly lower pulse energies (7 μJ DPSS laser versus 150 μJ nitrogen laser), in preliminary investigations the limit of detection was reduced by a factor of three for a typical FIA.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 016
KW - Immunoassay
KW - Fluoreszenz-Resonanz-Energie-Transfer
KW - Neodym-YAG-Laser
KW - 946 nm
KW - 473 nm
KW - 315 nm
KW - gepulster DPSS Laser
KW - sättigbarer Absorber
KW - fluorescence immunoassay
KW - 946 nm
KW - 473 nm
KW - 315 nm
KW - pulsed DPSS laser
Y1 - 2006
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-10150
ER -
TY - GEN
A1 - Lemke, Matthias
A1 - Fernández-Trujillo, Rebeca
A1 - Löhmannsröben, Hans-Gerd
T1 - In-situ LIF analysis of biological and petroleum-based hydraulic oils on soil
N2 - Absorption and fluorescence properties of 4 hydraulic oils (3 biological and 1 petroleum-based) were investigated. In-situ LIF (laser-induced fluorescence) analysis of the oils on a brown sandy loam soil was performed. With calibration, quantitative detection was achieved. Estimated limits of detection were below ca. 500 mg/kg for the petroleum-based oil and ca. 2000 mg/kg for one biological oil. A semi-quantitative classification scheme is proposed for monitoring of the biological oils. This approach was applied to investigate the migration of a biological oil in soil-containing compartments, namely a soil column and a soil bed.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 011
KW - in-situ
KW - optical oil sensor
KW - lubricants
KW - hydraulic oils
KW - soil
KW - laser induced
Y1 - 2005
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12268
ER -
TY - GEN
A1 - Ferenz, Hans-Jürgen
A1 - Peter, Martin G.
A1 - Berg, Dieter
T1 - Inhibition of farnesoic acid methyltransferase by sinefungin
N2 - Sinefungin inhibited the S-adenosylmethionine-dependent farnesoic acid methyltransferase in a cell-free system containing a homogenate of corpora allata from female locusts, Locusta migratoria. The enzyme catalyzed the penultimate step of juvenile hormone biosynthesis in the insects. Culturing corpora allata in the presence of sinefungin greatly suppressed juvenile hormone production. The following in vivo effects were visible after injection of the inhibitor: increase in mortality and reduction of total haemolymph protein liter and ovary fresh weight, as well as length of terminal oocytes. Attempts to reverse these effects by topical application of the juvenile hormone analog ZR-515 (methoprene) were only partly successful. Therefore, the in vivo effects may be due to a general inhibition of methyltransferase enzymes in the insect. Sinefungin appeared to be of potential interest as the first representative of a new class of insect growth regulators.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 077
KW - Juvenile hormone analogue
KW - Orthoptera
KW - Juvenile hormone
KW - Biosynthesis
KW - Enzyme
KW - Corpora allata
KW - In vitro
KW - Biological activity
KW - Enzyme inhibitor
Y1 - 1983
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17016
ER -
TY - GEN
A1 - Hörner, Gerald
A1 - Lau, Steffen
A1 - Kantor, Zoltan
A1 - Löhmannsröben, Hans-Gerd
T1 - Isotope selective analysis of CO2 with tunable diode laser (TDL) spectroscopy in the NIR
N2 - The performance of a home-built tunable diode laser (TDL) spectrometer, aimed at multi-line detection of carbon dioxide, has been evaluated and optimized. In the regime of the (3001)III / (000) band of 12CO2 around 1.6 μm, the dominating isotope species 12CO2, 13CO2, and 12C18O16O were detected simultaneously without interference by water vapor. Detection limits in the range of few ppmv were obtained for each species utilizing wavelength modulation (WM) spectroscopy with balanced detection in a long-path absorption cell set-up. High sensitivity in conjunction with high precision —typically ±1‰ and ±6‰ for 3% and 0.7% of CO2, respectively— renders this experimental approach a promising analytical concept for isotope-ratio determination of carbon dioxide in soil and breath gas. For a moderate 12CO2 line, the pressure dependence of the line profile was characterized in detail, to account for pressure effects on sensitive measurements.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 020
KW - Isotopenverhältnis
KW - Kohlendioxid
KW - Diodenlaserspektroskopie
KW - Isotope ratio
KW - carbon monoxide
KW - diode laser spectroscopy
Y1 - 2004
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-10167
ER -
TY - GEN
A1 - Lau, Steffen
A1 - Salffner, Katharina
A1 - Löhmannsröben, Hans-Gerd
T1 - Isotopic resolution of carbon monoxide and carbon dioxide by NIR diode laser spectroscopy
N2 - Near-infrared (NIR) absorption spectroscopy with tunable diode lasers allows the simultaneous detection of the three most important isotopologues of carbon dioxide (12CO2, 13CO2, 12C18O16O) and carbon monoxide (12CO, 13CO, 12C18O). The flexible and compact fiber-optic tunable diode laser absorption spectrometer (TDLAS) allows selective measurements of CO2 and CO with high isotopic resolution without sample preparation since there is no interference with water vapour. For each species, linear calibration plots with a dynamic range of four orders of magnitude and detection limits (LOD) in the range of a few ppm were obtained utilizing wavelength modulation spectroscopy (WMS) with balanced detection in a Herriott-type multipass cell. The high performance of the apparatus is illustrated by fill-evacuation-refill cycles.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 017
KW - Isotop
KW - Kohlenmonoxid
KW - Kohlendioxid
KW - Diodenlaserspektroskopie
KW - isotope
KW - carbon monoxide
KW - carbon dioxide
KW - diode laser spectroscopy
Y1 - 2006
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-10135
ER -
TY - GEN
A1 - Bringmann, Gerhard
A1 - Mutanyatta-Comar, Joan
A1 - Maksimenka, Katja
A1 - Wanjohi, John M.
A1 - Heydenreich, Matthias
A1 - Brun, Reto
A1 - Müller, Werner E. G.
A1 - Peter, Martin
A1 - Midiwo, Jacob O.
A1 - Yenesew, Abiy
T1 - Joziknipholones A and B : the First Dimeric Phenylanthraquinones, from the Roots of Bulbine frutescens
N2 - From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-configuration (i.e., with the acetyl portions below the anthraquinone plane) at both axes in the case of joziknipholone A, whereas in joziknipholone B, the knipholone part was found to be M-configured. Joziknipholones A and B are active against the chloroquine resistant strain K1 of the malaria pathogen, Plasmodium falciparum, and show moderate activity against murine leukemic lymphoma L5178y cells.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 104
KW - antimalarial activity
KW - chirality
KW - joziknipholones
KW - natural products
KW - structure elucidation
Y1 - 2008
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-42638
ER -