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 - Biddle, M. B.
A1 - Rickert, S. E.
A1 - Lando, J. B.
A1 - Laschewsky, André
T1 - The use of the Langmuir-Blodgett technique to obtain ultra-thin polar films
N2 - The piezoelectric and pyroelectric properties of oriented films possessing dipole moments are increasingly being used in pressure, acoustic, thermal and optical devices. The performance of these devices in many applications may be enhanced by thin-film technology.The developing Langmuir-Blodgett thin-film deposition technique offers the opportunity to obtain highly oriented and uniform organic-based films in the 10–5000 nm thickness range. Special techniques must be used, however, to assemble these molecules in such a way as to result in polar multilayer films. Several possible deposition techniques are investigated, with one resulting in a polar and pyroelectric film about 50 nm thick.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 098
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17185
ER -
TY - GEN
A1 - Tsukruk, Vladimir
A1 - Mischenko, Nikolay
A1 - Köberle, Peter
A1 - Laschewsky, André
T1 - The structural order of some novel ionic polymers; 2. : Models of molecular packing
N2 - The molecular packing and spatial correlations of two isomeric zwitterionic polymethacrylates and one polyacrylate analog are studied by means of X-ray analysis and conformational calculations. The analysis of the correlation functions and density distribution profiles suggest a double-layered molecular packing which is discussed for the three polymers investigated, with respect to their different chemical structures. Whereas the zwitterionic polymethacrylates studied exhibit liquid-like short-range order, the polyacrylate analog exhibits an ordered double-layered superstructure.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 096
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17256
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 - Lupo, Donald
A1 - Prass, Werner
A1 - Scheunemann, Ude
A1 - Laschewsky, André
A1 - Ringsdorf, Helmut
A1 - Ledoux, Isabelle
T1 - Second-harmonic generation in Langmuir-Blodgett monolayers of stilbazium salt and phenylhydrazone dyes
N2 - Contents: 1. INTRODUCTION 2. SYNTHESIS OF THE COMPOUNDS 3. PREPARATION AND CHARACTERIZATION OF MONOLAYERS A. Monolayer Isotherms B. Langmuir-Blodgett Monolayer Films 4. EXPERIMENTAL SETUP FOR NONLINEAR MEASUREMENTS 5. NONLINEAR OPTICAL PROPERTIES 6. DISCUSSION 7. CONCLUSION
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 094
Y1 - 1988
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17401
ER -
TY - GEN
A1 - Rozanski, Stanislaw A.
A1 - Kremer, Friedrich
A1 - Köberle, Peter
A1 - Laschewsky, André
T1 - Relaxation and charge transport in mixtures of zwitterionic polymers and inorganic salts
N2 - Dielectric spectroscopy is employed to analyze the molecular dynamics and the charge transport in mixtures of zwitterionic polymers of the type poly{3 [N(-methacryloyloxyalkyl)] N, [N-dimethylammonio propanesulfonate] with sodium iodide in the frequency range of 10²Hz-10(up)7 Hz and in the temperature range of 110 K-400 K. The amount of inorganic salt added varies from 0-200 mol-% relative to the number of zwitterionic groups present in the polymer, contributing strongly to the conductivity. One relaxation process is observed whose relaxation rate depends strongly on the length of the aliphatic spacer between the polymethacrylate main chain and the zwitterionic group. Exhibiting an Arrhenius-like temperature depence with activation energy EA = 47 KJ/mol, this relaxation process is assigned to fluctuation of the quaternary ammonium groups in the side chains. At higher temperatures, the dielectric properties and the conductivity are primarily dominated by the mobile inorganic ions: conductivity strongly depends on the salt concentration, showing a pronounced electrode polarization effect. The frequency and salt concentration, dependences of the conductivity can be quantitatively described as hopping of charge carriers being subject to spatially randomly varying energy barriers. For the low-frequency regime and for the critical frequency marking the onset of the conductivity's dispersion, the Barton-Nakajima-Namikawa (BNN) relationship is fulfilled.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 093
Y1 - 1995
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17438
ER -
TY - GEN
A1 - Laschewsky, André
A1 - Schulz-Hanke, Wolfgang
T1 - Ring-opening metathesis polymerization of amphiphilic norbornenes functionalized with non-linear optical (NLO) chromophores
N2 - Contents: Potential of amphiphilic NLO polymers Ring-opening metathesis polymerization (ROMP) Properties of the polymers Monolayer properties Experimental part - Methods - Materials - Analytical data - General polymerization procedure Conclusions
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 092
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-26917
ER -
TY - GEN
A1 - Anton, Peter
A1 - Laschewsky, André
T1 - Zwitterionic polysoaps with reduced density of surfactant side groups
N2 - Several zwitterionic polymers were prepared by radical homopolymerization of surfactant monomers which bear diallyl, diene or vinylcyclopropane moieties. These polymer systems were complemented by alternating copolymers of appropriate zwitterionic vinyl compounds. Thus, polymers with reduced (as compared with simple vinylic homopolymers, or statistical copolymers) and well defined density of surfactant side groups are obtained. The solubilities found for these polymers are dominated by polymer geometry rather than by the balance of hydrophilic and hydrophobic fragments, thus corroborating a main-chain spacer model proposed recently. All water-soluble polymers exhibit characteristic features of classical polysoaps, as shown by surface tension measurements and by solubilization of hydrophobic dyes. In contrast, the water-insoluble copolymers are capable to form stable monolayers at the air-water interface.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 091
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17301
ER -
TY - GEN
A1 - Anton, Peter
A1 - Köberle, Peter
A1 - Laschewsky, André
T1 - Recent developments in the field of micellar polymers
N2 - This article describes recent achievements in the field of micellar polymers, or polysoaps. Taking advantage of zwitterionic model polymers, systematic variations of the molecular architecture have provided an improved understanding of the relationship between the molecular structure of the polymers and their key properties such as surface activity and solubilization capacity. Useful rules are established, which take into account much of the previous data in the literature.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 090
Y1 - 1993
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17263
ER -
TY - GEN
A1 - Köberle, Peter
A1 - Laschewsky, André
A1 - Tsukruk, Vladimir
T1 - The structural order of some novel ionic polymers : 1. X-ray scattering studies
N2 - A set of novel zwitterionic side-chain polyacrylates and polymethacrylates is studied by X-ray scattering. The structural order both in the short-range and long-range scale is investigated. The influence of the polymer backbone, of different locations of the ionic groups in isomeric polymers, of bound water and of added inorganic salts on the bulk structures is studied, and the observed rearrangements are analysed.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 089
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17247
ER -
TY - GEN
A1 - Anton, Peter
A1 - Laschewsky, André
T1 - Polysoaps via alternating olefin/SO2 copolymers
N2 - Contents: Introduction Results and discussion - Monomers studied - Monomer properties - Polymerization, copolymer composition and general properties - Polymer properties in aqueous solution Conclusion Experimental part - Materials - Copolymerization with S02 (typical procedure) - Methods
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 088
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17216
ER -
TY - GEN
A1 - Laschewsky, André
T1 - Molecular concepts, self-organisation and properties of polysoaps
N2 - The article reviews water-soluble polymers characterized by surfactant side chains, and related amphiphilic polymers. Various synthetic approaches are presented, and rules for useful molecular architectures are given. Models for the self-organization of such polymers in water are presented comparing them with the micellization of low molecular weight surfactants. Highlighting key properties of aqueous polysoap solutions such as viscosity, surface tension and solubilization power, some structure-property relationships are established. Further, the formation of mesophases and of superstructures in bulk is addressed. Finally, the functionalization of polysoaps, and potential applications are discussed.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 087
Y1 - 1995
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-26895
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 - Cochin, Didier
A1 - Hendlinger, P.
A1 - Laschewsky, André
T1 - Polysoaps with fluorocarbon hydrophobic chains
N2 - A series of amphiphilic copolymers is prepared by copolymerization of choline methacrylate with 1,1,2,2-tetrahydroperfluorooctyl methacrylate in varying amounts. The copolymers bearing fluorocarbon chains are studied concerning their effects on viscosity, solubilization and surface activity in aqueous solution, exhibiting a general behavior characteristic for polysoaps. The results are compared with the ones obtained for an analogous series of amphiphilic copolymers bearing hydrocarbon chains.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 085
KW - Amphiphilic polymers
KW - fluorocarbon polymers
KW - associating polymers
KW - polysoaps
Y1 - 1995
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17347
ER -
TY - GEN
A1 - Anton, Peter
A1 - Laschewsky, André
A1 - Ward, M. D.
T1 - Solubilization control by redox-switching of polysoaps
N2 - Reversible changes in the self-organization of polysoaps may be induced by controlling their charge numbers via covalently bound redox moieties. This is illustrated with two viologen polysoaps, which in response to an electrochemical stimulus, change their solubility and aggregation in water, leading from homogeneously dissolved and aggregated molecules to collapsed ones and vice verse. Using the electrochemical quartz crystal microbalance (EQCM), it could be shown that the reversibility of this process is better than 95% in 16 cycles.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 084
KW - Quartz Crystal
KW - microbalance
KW - films
KW - Electrochemistry
KW - viologen
Y1 - 1995
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17336
ER -
TY - GEN
A1 - Anton, Peter
A1 - Laschewsky, André
T1 - Solubilization by polysoaps
N2 - The aqueous solubilization power of several series of micellar homopolymers and copolymers (polysoaps) is investigated. Using five insoluble or poorly water-soluble dyes, comparisons of the capacities are made with respect ot the influence of structural variables such as the polymer backbone, the polymer geometry, the comonomer content, and the charge of the hydrophilic group. Some guidelines for polysoap structures suited for efficient solubilization are established. Noteworthy is that the solubilization capacities of the polysoaps are neither linked to the ability to reduce the surface tension of water, nor to the polarity of the solubilization sites deduced from spectroscopic probes.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 083
KW - Micellar polymers
KW - polysoaps
KW - solubilization
Y1 - 1994
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17327
ER -
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 - Embs, Frank
A1 - Funhoff, Dirk
A1 - Laschewsky, André
A1 - Licht, Ulrike
A1 - Ohst, Holger
A1 - Prass, Werner
A1 - Ringsdorf, Helmut
A1 - Wegner, Gerhard
A1 - Wehrmann, Rolf
T1 - Preformed polymers for Langmuir-Blodgett films- molecular concepts
N2 - The use of preformed polymers for the preparation of Langmuir-Blodgett (LB) multilayers is reviewed. Principles for polymer self-organization are outlined and the appropriate molecular designs are discussed. Recent developments in the different classes of polymers for LB multilayers are presented, and their outstanding properties highlighted.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 081
KW - Amphiphilic Polymers
KW - Rod-like Polymers
KW - LCPs
KW - Stability of LB Films
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17196
ER -
TY - GEN
A1 - Erdelen, C.
A1 - Laschewsky, André
A1 - Ringsdorf, H.
A1 - Schneider, J.
A1 - Schuster, A.
T1 - Thermal behaviour of polymeric Langmuir-Blodgett multilayers
N2 - Langmuir-Blodgett multilayers of hydrocarbon and fluorocarbon polymers with hydrophilic spacer, lipid-polyelectrolyte complexes and mesogenic polymers have been prepared. The thermal behaviour of the multilayers was studied by small angle X-ray scattering, IR and UV—visible spectroscopy. Good thermal stabilities were found for the various classes of polymers. In addition, for both complexed multilayers and mesogenic polymer films, reorientation processes were observed.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 080
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17378
ER -
TY - GEN
A1 - Albrecht, O.
A1 - Cumming, W.
A1 - Kreuder, W.
A1 - Laschewsky, André
A1 - Ringsdorf, Helmut
T1 - Monolayers of rod-shaped and disc-shaped liquid crystalline compounds at the air-water interface
N2 - Calamitic (rod-shaped) and discotic (disc-shaped) thermotropic liquid crystalline (LC) compounds were spread at the air-water interface, and their ability to form monolayers was studied. The calamitic LCs investigated were found to form monolayers which behave analogously to conventional amphiphiles such as fatty acids. The spreading of the discotic LCs produced monolayers as well, but with a behaviour different from classical amphiphiles. The areas occupied per molecule are too small to allow the contact of all hydrophilic groups with the water surface and the packing of all hydrophobic chains. Various molecular arrangements of the discotics at the water surface to fit the spreading data are discussed.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 079
KW - Monolayers
KW - liquid crystals
KW - discotics
Y1 - 1986
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17124
ER -
TY - GEN
A1 - Koch, Horst
A1 - Laschewsky, André
A1 - Ringsdorf, Helmut
A1 - Teng, Kang
T1 - Photodimerization and photopolymerization of amphiphilic cinnamic acid derivatives in oriented monolayers, vesicles and solution
N2 - Cinnamic acid moieties were incorporated into amphiphilic compounds containing one and two alkyl chains. These lipid-like compounds with photoreactive units undergo self-organization to form monolayers at the gas-water interface and bilayer structures (vesicles) in aqueous solutions. The photoreaction of the cinnamic acid moiety induced by 254 nm UV light was investigated in the crystalline state, in monolayers, in vesicles and in solution in organic solvents. The single-chain amphiphiles undergo dimerization to yield photoproducts with twice the molecular weight of the corresponding monomers in organized systems. The photoreaction of amphiphiles containing two cinnamic acid groups occurs via two mechanisms: The intramolecular dimerization produces bicycles, with retention of the molecular weight of the corresponding monomer. The intermolecular reaction leads to oligomeric and polymeric photoproducts. In contrast to the single-chain amphiphiles, photodimerization processes of lipoids containing two cinnamic acid moieties also occur in solution in organic solvents.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 078
Y1 - 1986
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17111
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 - Ferenz, Hans-Jörg
A1 - Peter, Martin G.
T1 - The inhibitory effect of sinefungin on juvenile hormone biosynthesis and development in locusts
N2 - The antibiotic fungal metabolite sinefungin is a potent inhibitor of S-adenosylmethionine-acceptor methyltransferases. Its effect on insect metabolism and especially on corpora allata farnesoic acid methyltransferase, which catalyzes the penultimate step of juvenile hormone biosynthesis, was investigated in Locusta migratoria. Injection of sinefungin results in a delay of imaginal molt and in suppression of ovary development. Isolated corpora allata are unable to synthesize juvenile hormone III in the presence of more than 1.0 mM sinefungin. In a cell-free system containing the S-adenosylmethionine-dependent farnesoic acid methyltransferase from corpora allata sinefungin is a competitive inhibitor of the synthesis of methylfarnesoate with Ki of 1 μM.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 076
KW - Locust
KW - sinefungin
KW - O-methyltransferase
KW - juvenile hormone biosynthesis
Y1 - 1987
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-16811
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 - 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 - GEN
A1 - Laschewsky, André
T1 - Monolayers and Langmuir-Blodgett multilayers of discotic liquid crystals?
N2 - Contents: 1. Discotic Liquid Crystals 2. Monolayers and Langmuir-Blodgett Multilayers 3. Theoretical Considerations on the Molecular Packing of Discotic LCs in Monolayers and Multilayers 4. Spreading Experiments with Discotic LCs 5. LB-Multilayers of Discotic LCs 6. Polymeric Discotic LCs 7. Summary
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 061
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17396
ER -
TY - GEN
A1 - Laschewsky, André
A1 - Paulus, Wolfgang
A1 - Ringsdorf, Helmut
A1 - Schuster, A.
A1 - Frick, G.
A1 - Mathy, A.
T1 - Mixed polymeric monolayers and Langmuir-Blodgett multilayers with functional low molecular weight guest compounds
N2 - Mixed monolayers and Langmuir-Blodgett multilayers of functional low molecular weight guest compounds, especially nonlinear optical (NLO) dyes, within the matrix of an amphotropic spacer polymer have been prepared. The polymer matrix enabled the transfer of guest compounds not capable of self-organizing at the air-water interface by themselves. The structure of the LB multilayers and the transfer process were studied by small angle X-ray scattering and UV-visible spectroscopy. Good NLO coefficients were found in the mixed films.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 060
Y1 - 1992
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17233
ER -
TY - GEN
A1 - Laschewsky, André
T1 - Oligoethyleneoxide spacer groups in polymerizable surfactants
N2 - Cationic and zwitterionic polymerizable surfactants bearing tri- and tetraethyleneglycol spacer groups between the polymerizable moiety and the surfactant structure were prepared and polymerized. Monomers and polymers were investigated with respect to their aggregation behavior in aqueous systems and compared to analogous monomers and polymers lacking spacer groups. In the case of the monomeric surfactants, the spacer groups depress both the Kraffttemperature and the critical micelle concentration. the area occupied per molecule at the air-water interface is substantially enlarged by the spacers, whereas the depression of surface tension is nearly constant. Although the monomers with and without spacers are true surfactants, all the polymers are water-insoluble, but form monomolecular layers at the air-water interface. In analogy to the monomer behavior, the incorporation of the spacer groups increases the area occupied per repeat unit at the air-water interface substantially, but hardly affects the surface activity.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 059
KW - Polymerizable surfactant
KW - polysoap
KW - sulfobetain
KW - spacer
KW - micelle
KW - monolayer
Y1 - 1991
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17221
ER -
TY - GEN
A1 - Laschewsky, André
A1 - Ringsdorf, H.
T1 - Polymerization of amphiphilic dienes in Langmuir-Blodgett multilayers
N2 - Amphiphilic derivatives of octadiene and docosadiene were investigated in monolayers and Langmuir-Blodgett multilayers, with respect to their self-organization and their polymerization behavior. All amphiphiles investigated form monolayers. However, only acid and alcohol derivatives were able to build up multilayers. Those multilayers are rapidly photopolymerized in the layers via a two-step process: Irradiation with long-wavelength UV light yields soluble polymers, whereas additional irradiation with sfiort-wavelength UV light produces insoluble and presumably cross-linked polymers. The reaction meclianism is discussed according to the polymer characterization by UV spectroscopy, small-angle X-ray scattering, NMR spectroscopy, and gel permeation chromatography. All multilayers undergo structural changes during the polymerization; substantial changes result in defects in the polymerized layers as observed by scanning electron microscopy. In contrast to the acids and alcohols, the deposition of monolayers of the aldehyde derivatives did not yield well-ordered multilayers, but rather amorphous films. In this different film structure, the photopolymerization process differs from the one observed in multilayers.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 058
Y1 - 1988
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17176
ER -
TY - GEN
A1 - Laschewsky, André
A1 - Ringsdorf, H.
A1 - Schmidt, G.
A1 - Schneider, J.
T1 - Self-organization of polymeric lipids with hydrophilic spacers in side groups and main chain : investigation in monolayers and multilayers
N2 - Several polymerizable lipids were synthesized and polymerized to amphiphilic homopolymers and to copolymers with the help of hydrophilic comonomers. The self-organization of these polymeric lipids was investigated in monolayers and Langmuir-Blodgett multilayers. The self-organization of these polymers in model membranes is due to hydrophilic spacer groups in the amphiphilic side groups as well as to hydrophilic spacer groups in the polymer backbone. Thus, highly ordered monolayers and LB-multilayers are easily obtained.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 057
Y1 - 1987
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17147
ER -
TY - GEN
A1 - Laschewsky, André
A1 - Ringsdorf, H.
A1 - Schneider, J.
T1 - Oriented supramolecular systems-polymeric monolayers and multilayers from prepolymerized amphiphiles
N2 - Oriented polymeric membranes were originally prepared by polymerization or polycondensation of preoriented monomers. The introduction of hydrophilic spacer groups into the polymeric amphiphiles allowed the formation of highly ordered systems (monolayers, liposomes, multilayers) from prepolymerized amphiphiles: due to the partial decoupling of the different mobilities and orientation tendencies of the polymer chain and the amphiphilic side groups, these polymers are able to self-organize. In monolayer experiments the high order of these membranes could be demonstrated by their surface pressure area-diagrams. In addition the combination of order and mobility of these spacer groups containing polymeric amphiphiles allowed the formation of Langmuir-Blodgett-multilyers with a high layer correlation. Thus, disturbancies in highly oriented layers can be avoided normally taking place during the polymerization reaction (e.g. contractions) or oriented monomeric layers.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 056
Y1 - 1986
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17131
ER -
TY - GEN
A1 - Laschewsky, André
A1 - Ringsdorf, H.
A1 - Schmidt, G.
T1 - Polymerization of hydrocarbon and fluorocarbon amphiphiles in Langmuir-Blodgett multilayers
N2 - Langmuir-Blodgett multilayers of polymerizable carboxylic acids with hydrocarbon or fluorocarbon chains were prepared. The multilayers were polymerized by UV light and the reactions were studied by UV/visible spectroscopy. The polyreactions strongly influence the multilayer structures which were investigated by X-ray small-angle scattering and scanning electron microscopy. The spreading behaviour of the monomers, the preparation of multilayers, their reactivities in multilayers and structural effects caused by the polyreactions are discussed with regard to the hydrophilic head groups, the polymerizable groups and the hydrophobic chains.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 055
Y1 - 1985
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17096
ER -
TY - GEN
A1 - Peter, Martin G.
A1 - Förster, Hans
T1 - On the structure of Eumelanins : identification of constitutional patterns by solid-state NMR spectroscopy
N2 - Aus dem Inhalt: Melanins are complex polyphenolic polymers. They are usually formed in nature by enzyme-catalyzed oxidative polymerization of o-diphenols. The deep black eumelanins, derived from Dopa 1 or dopamine 3, are distinguished from the yellow to brown phaeomelanins obtained from Dopa in the presence of cysteine. Characteristic of eumelanins are the indole units, which are formed from catecholamines by intramolecular addition of the amino groups to the oxidatively generated o-quinones. [...]
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 053
Y1 - 1989
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17027
ER -
TY - GEN
A1 - Peter, Martin G.
T1 - Products of in vitro oxidation of N-acetyldopamine as possible components in the sclerotization of insect cuticle
N2 - [1-14C]-N-Acetyldopamine (NADA) was oxidized in the presence of methyl [3-3H]-β-alanate with mushroom tyrosinase. The complex mixture of reaction products was partly resolved by chromatographic procedures and analyzed by spectroscopic methods. Methyl-β-alanate is incorporated to only a small extent into oxidation products of NADA which inter alia are presumed to be oligomeric hydroxyquinones. After oxidation of [1-14C, 2-3H]-NADA with preparations from tanning Manduca sexta pupal cuticle, N-acetylnoradrenalin was identified as one of the products. Binding of radioactivity to melanin-like material was also observed. These results suggest that oxidation products different from those formulated usually for the crosslinkages between protein amino groups and N-acetyldopaquinone are deposited in darkly brown coloured insect cuticles during sclerotization.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 041
KW - N-acetyldopamine
KW - sclerotization
KW - tyrosinase; o-quinones
KW - tanning agents
Y1 - 1980
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-16759
ER -
TY - THES
A1 - Frankovitch, Christine Marie
T1 - Optical methods for monitoring biological parameters of phototropic microorganisms during cultivation
T1 - Optische Verfahren zur Beobachtung biologischer Parameter während der Kultivierung phototropischer Mikroorganismen
N2 - Phototropic microalgae have a large potential for producing valuable substances for the feed, food, cosmetics, pigment, bioremediation, and pharmacy industries as well as for biotechnological processes. Today it is estimated that the microalgal aquaculture worldwide production is 5000 tons of dry matter per year (not taking into account processed products) making it an approximately $1.25 billion U.S. per year industry. In this work, several spectroscopic techniques were utilized for the investigation of microalgae cells. Specifically, photondensity wave spectroscopy was applied as a technique for the on-line observation of the culture. For effective evaluation of the photosynthetic growth processes, fast and non-invasive sensor systems that analyze the relevant biological and technical process parameters are preferred. Traditionally, the biomass in a photobioreactor is quantified with the help of turbidimetry measurements, which require extensive calibration. Another problem frequently encountered when using spectral analysis for investigating solutions is that samples of interest are often undiluted and highly scattering and do not adhere to Beer-Lambert's law. Due to the fluorescence properties of chlorophyll, fluorescence spectroscopy techniques including fluorescence lifetime imaging and single photon counting could be applied to provide images of the cells as well as determine the effects of excitation intensity on the fluorescence lifetime, which is an indicator of the condition of the cell. A photon density wave is a sinusoidally intensity-modulated optical wave stemming from a point-source of light, which propagates through diffuse medium and exhibits amplitude and phase variations. Light propagation though strongly scattering media can be described by the P1 approximation to the Boltzmann transport equation. Photon density wave spectroscopy enables the ability to differentiate between scattered and absorbed light, which is desired so that an independent determination of the reduced scattering and absorption coefficients can be made. The absorption coefficient is related to the pigment content in the cells, and the reduced scattering coefficient can be used to characterize physical and morphological properties of the medium and was here applied for the determination of the average cell size.
N2 - Phototropische Mikroalgen besitzen ein großes Potential für die Herstellung von wertvollen Substanzen sowohl für die Futtermittel-, Lebensmittel-, kosmetische und pharmazeutische Industrie, als auch für die Farbstoffsynthese. Heutzutage werden schätzungsweise 5000 Tonnen Mikroalgen Trockensubstanz pro Jahr mit einem Jahresumsatz von 1,25 Mrd. US-Dollar produziert. In dieser Arbeit wurden diverse spektroskopische Untersuchungsmethoden für die Betrachtung der Zellen verwendet. Die Photonendichtewellenspektroskopie (PDW) fand dabei insbesondere bei der on-line Beobachtung der Zellen Anwendung. Voraussetzungen für die effektive Beobachtung von photosynthetischen Wachstumsprozessen sind schnell und nicht-invasiv arbeitende Sensoren. Normalerweise wird die dabei zu untersuchende Biomasse in einem Photobioreaktor mittels Trübungsmessungen quantifiziert. Dies setzt jedoch eine sehr aufwendige Kalibration voraus. Da diese Proben zusätzlich meist in unverdünnter Form vorliegen, streuen sie stark und folgen daher nicht dem Lambert-Beer'schen Gesetz. Aufgrund der Fluoreszenzeigenschaften des Chlorophylls können fluoreszenzspektroskopische Methoden wie fluorescence lifetime imaging microscopy (FLIM) und time correlated single photon counting (TCSPC) angwendet werden. Diese Methoden werden dabei für die visuelle Darstellung der Zellen und für die Messung der Fluoreszenzlebenszeit genutzt. Eine Photondichtewelle ist eine sinusförmig intensitätsmodulierte optische Welle, die sich, ausgehend von einer punktförmigen Lichtquelle, durch das untersuchte Medium ausbreitet, wobei sich Phase und Amplitude der Welle verändern. Die Ausbreitung der Welle wird von der P1-Näherung der Boltzmann-Transport-Gleichung beschrieben. Mittels PDW kann zwischen streuenden und absorbierenden Eigenschaften von trüben Probe unterschieden werden. Dies erlaubt die Absolutbestimmung des Absorptions- und reduzierten Streukoeffizienten, die für die Qualifizierung der Probe, insbesondere der Teilchengrößenbestimmung, herangezogen werden.
KW - Photonendichtewellen
KW - Mikroalgen
KW - Photon density waves
KW - Microalgae
KW - On.Line Monitoring
Y1 - 2007
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-15403
ER -
TY - GEN
A1 - Kaafarani, Bilal R.
A1 - Wex, Brigitte
A1 - Strehmel, Bernd
A1 - Neckers, Douglas C.
T1 - Structural concept for fluorinated Y-enynes with solvatochromic properties
N2 - An approach to the development of fluorescent probes to follow polymerizations in situ using fluorinated cross-conjugated enediynes (Y-enynes) is reported. Different substitution patterns in the Y-enynes result in distinct solvatochromic behavior. β,β-Bis(phenylethynyl)pentafluorostyrene 7, which bears no donor substituents and only fluorine at the styrene moiety, shows no solvatochromism. Donor substituted β,β-bis(3,4,5-trimethoxyphenylethynyl) pentafluorostyrene 8 and β,β-bis(4-butyl-2,3,5,6-tetrafluorophenylethynyl)-3,4,5-trimethoxystyrene 9 exhibit solvatochromism upon change of solvent polarity. Y-enyne 8 showed the largest solvatochromic shift (94 nm bathochromic shift) upon changing solvent from cyclohexane to acetonitrile. A smaller solvatochromic response (44 nm bathochromic shift) was observed for 9. Lippert–Mataga treatment of 8 and 9 yields slopes of -10,800 and -6,400 cm -1, respectively. This corresponds to a change in dipole moment of 9.6 and 6.9 D, respectively. The solvatochromic behavior in 8 and 9 supports the formation of an intramolecular charge transfer (ICT) state. The low fluorescence quantum yields are caused by competitive double bond rotation. The fluorescence decay time of 9 decreases in methyltetrahydrofuran from 2.1 ns at 77 K to 0.11 ns at 200 K. Efficient single bond rotation in 9 was frozen at -50 °C in a configuration in which the trimethoxyphenyl ring is perpendicular to the fluorinated rings. 7–9 are photostable compounds. The X-ray structure of 7 shows it is not planar and that its conjugation is distorted. Y-enyne 7 stacks in the solid state showing coulombic, actetylene–arene, and fluorine–π interactions.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 027
Y1 - 2002
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-13168
ER -
TY - GEN
A1 - Reich, Oliver
A1 - Löhmannsröben, Hans-Gerd
A1 - Schael, Frank
T1 - Optical sensing with photon density waves: investigation of model media
N2 - Investigations with frequency domain photon density waves allow elucidation of absorption and scattering properties of turbid media. The temporal and spatial propagation of intensity modulated light with frequencies up to more than 1 GHz can be described by the P1 approximation to the Boltzmann transport equation. In this study, we establish requirements for the appropriate choice of turbid model media and characterize mixtures of isosulfan blue as absorber and polystyrene beads as scatterer. For these model media, the independent determination of absorption and reduced scattering coefficients over large absorber and scatterer concentration ranges is demonstrated with a frequency domain photon density wave spectrometer employing intensity and phase measurements at various modulation frequencies.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 026
Y1 - 2003
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-13147
ER -
TY - GEN
A1 - Engelhard, Sonja
A1 - Kumke, Michael Uwe
A1 - Löhmannsröben, Hans-Gerd
T1 - OPQS – optical process and quality sensing : exemplary applications in the beerbrewing and polyurethane foaming processes
N2 - Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near-infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 004
KW - process analytical technology
KW - beer
KW - biomass
KW - foam analysis
KW - NIR spectroscopy
KW - fluorescence quenching
KW - photon density wave spectroscopy
Y1 - 2006
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12191
ER -
TY - GEN
A1 - Schmälzlin, Elmar
A1 - Walz, Bernd
A1 - Klimant, Ingo
A1 - Schewe, Bettina
A1 - Löhmannsröben, Hans-Gerd
T1 - Monitoring hormone-induced oxygen consumption in the salivary glands of the blowfly, Calliphora vicina, by use of luminescent microbeads
N2 - The salivary glands of the blowfly were injected with luminescent oxygen-sensitive microbeads. The changes in oxygen content within individual gland tubules during hormone-induced secretory activity were quantified. The measurements are based on an upgraded phase-modulation technique, where the phase shift of the sensor phosphorescence is determined independently from concentration and background signals. We show that the combination of a lock-in amplifier with a fluorescence microscope results in a convenient setup to measure oxygen concentrations within living animal tissues at the cellular level.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 006
Y1 - 2006
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12206
ER -
TY - GEN
A1 - Hildebrandt, Nico
A1 - Charbonnière, Loïc J.
A1 - Ziessel, Raymond F.
A1 - Löhmannsröben, Hans-Gerd
T1 - Quantum dots as resonance energy transfer acceptors for monitoring biological interactions
N2 - Quantum dots (QDs) are common as luminescing markers for imaging in biological applications because their optical properties seem to be inert against their surrounding solvent. This, together with broad and strong absorption bands and intense, sharp tuneable luminescence bands, makes them interesting candidates for methods utilizing Forster Resonance Energy Transfer (FRET), e. g. for sensitive homogeneous fluoroimmunoassays (FIA). In this work we demonstrate energy transfer from Eu3+-trisbipyridin (Eu-TBP) donors to CdSe-ZnS-QD acceptors in solutions with and without serum. The QDs are commercially available CdSe-ZnS core-shell particles emitting at 655 nm (QD655). The FRET system was achieved by the binding of the streptavidin conjugated donors with the biotin conjugated acceptors. After excitation of Eu-TBP and as result of the energy transfer, the luminescence of the QD655 acceptors also showed lengthened decay times like the donors. The energy transfer efficiency, as calculated from the decay times of the bound and the unbound components, amounted to 37%. The Forster-radius, estimated from the absorption and emission bands, was ca. 77Å. The effective binding ratio, which not only depends on the ratio of binding pairs but also on unspecific binding, was obtained from the donor emission dependent on the concentration. As serum promotes unspecific binding, the overall FRET efficiency of the assay was reduced. We conclude that QDs are good substitutes for acceptors in FRET if combined with slow decay donors like Europium. The investigation of the influence of the serum provides guidance towards improving binding properties of QD assays.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 012
Y1 - 2006
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12213
ER -
TY - GEN
A1 - Schuler, Benjamin
A1 - Lipman, Everett A.
A1 - Steinbach, Peter J.
A1 - Kumke, Michael Uwe
A1 - Eaton, William A.
T1 - Polyproline and the "spectroscopic ruler" revisited with single-molecule fluorescence
N2 - To determine whether Förster resonance energy transfer (FRET) measurements can provide quantitative distance information in single-molecule fluorescence experiments on polypeptides, we measured FRET efficiency distributions for donor and acceptor dyes attached to the ends of freely diffusing polyproline molecules of various lengths. The observed mean FRET efficiencies agree with those determined from ensemble lifetime measurements but differ considerably from the values expected from Förster theory, with polyproline treated as a rigid rod. At donor–acceptor distances much less than the Förster radius R0, the observed efficiencies are lower than predicted, whereas at distances comparable to and greater than R0, they are much higher. Two possible contributions to the former are incomplete orientational averaging during the donor lifetime and, because of the large size of the dyes, breakdown of the point-dipole approximation assumed in Förster theory. End-to-end distance distributions and correlation times obtained from Langevin molecular dynamics simulations suggest that the differences for the longer polyproline peptides can be explained by chain bending, which considerably shortens the donor–acceptor distances.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 008
KW - Förster resonance energy transfer
KW - molecular dynamics
KW - polypeptide
KW - FRET
Y1 - 2005
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12229
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 - 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 - 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 - Kumke, Michael Uwe
A1 - Frimmel, Fritz Hartmann
T1 - Stationary and time-resolved fluorescence for humic substances characterization
N2 - Steady-state and time-resolved fluorescence methods were applied to investigate the fluorescence properties of humic substances of different origins. Using standard 2D emission and total luminescence spectra, fluorescence maxima, the width of the fluorescence band and a relative fluorescence quantum efficiency were determined. Different trends for fulvic acids and humic acids were observed indicating differences in the heterogeneity of the sample fractions. The complexity of the fluorescence decay of humic substances is discussed and compared to simple model compounds. The effect of oxidation of humic substances on their fluorescence properties is discussed as well.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 014
Y1 - 2002
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12353
ER -
TY - GEN
A1 - Dosche, Carsten
A1 - Löhmannsröben, Hans-Gerd
A1 - Bieser, A.
A1 - Dosa, P. I.
A1 - Han, S.
A1 - Iwamoto, M.
A1 - Schleifenbaum, A.
A1 - Vollhardt, K. Peter C.
T1 - Photophysical properties of [N]phenylenes
N2 - In the present study, photophysical properties of [N]phenylenes were studied by means of stationary and time-resolved absorption and fluorescence spectroscopy (in THF at room temperature). For biphenylene (1) and linear [3]phenylene (2a), internal conversion (IC) with quantum yields ΦIC > 0.99 is by far the dominant mechanism of S1 state deactivation. Angular [3]phenylene (3a), the zig-zag [4]- and [5]phenylenes (3b), (3c), and the triangular [4]phenylene (4) show fluorescence emission with fluorescence quantum yieds and lifetimes between ΦF = 0.07 for (3a) and 0.21 for (3c) and τF = 20 ns for (3a) and 81 ns for (4). Also, compounds (3) and (4) exhibit triplet formation upon photoexcitation with quantum yields as high as ΦISC = 0.45 for (3c). The strong differences in the fluorescence properties and in the triplet fromation efficiencies between (1) and (2a) on one hand and (3) and (4) on the other are related to the remarkable variation of the internal conversion (IC) rate constants kIC. A tentative classification of (1) and (2a) as “fast IC compounds”, with kIC > 109 s-1, and of (3) and (4) as “slow IC compounds”, with kIC ≈ 107 s-1, is suggested. This classification cannot simply be related to Hückel’s rule-type concepts of aromaticity, because the group of “fast IC compounds” consists of “antiaromatic” (1) and “aromatic” (2a), and the group of “slow IC compounds” consists of “antiaromatic” (3b), (4) and “aromatic” (3a), (3c). The IC in the [N]phenylenes is discussed within the framework of the so-called energy gap law established for non-radiative processes in benzenoid hydrocarbons.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 001
Y1 - 2002
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-11936
ER -
TY - GEN
A1 - Löhmannsröben, Hans-Gerd
A1 - Beitz, Toralf
A1 - Luadien, Robert
A1 - Schultze, Rainer
T1 - Laser-based ion mobility spectrometry for sensing of aromatic compounds
N2 - The drift time spectra of polycyclic aromatic hydrocarbons (PAH), alkylbenzenes and alkylphenylethers were recorded with a laser-based ion mobility (IM) spectrometer. The ion mobilities of all compounds were determined in helium as drift gas. This allows the calculation of the diffusion cross sections (Omegacalc) on the basis of the exact hard sphere scattering model (EHSSM) and their comparison with the experimentally determined diffusion cross sections (Omegaexp). These Omegaexp/Omegacalc-correlations are presented for molecules with a rigid structure like PAH and prove the reliability of the theoretical model and experimental method. The increase of the selectivity of IM spectrometry is demonstrated using resonance enhanced multiphoton ionisation (REMPI) at atmospheric pressure, realized by tuneable lasers. The REMPI spectra of nine alkylbenzenes and alkylphenylethers are investigated. On the basis of these spectra, the complete qualitative distinction of eight compounds in a mixture is shown. These experiments are extended to alkylbenzene isomer mixtures.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 003
KW - Laser
KW - REMPI
KW - Ion mobility spectrometry
KW - PAH
Y1 - 2004
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-11892
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 - 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 - Hörner, Gerald
A1 - Lau, Steffen
A1 - Löhmannsröben, Hans-Gerd
T1 - NIR-diode laser spectroscopy for isotope-selective sensing of soil-respired carbon dioxide
N2 - The performance of a home-built tunable diode laser (TDL) spectrometer has been optimized regarding multi-line detection of carbon dioxide in natural gases. 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. In contrast to most established techniques, selective measurements are performed without any sample preparation. This is possible since the CO2 detection is free of interference from water, ubiquitous in natural gases. Detection limits in the range of a few ppmv were obtained for each species utilizing wavelength modulation (WM) spectroscopy with balanced detection in a long-path absorption cell set-up. Linear calibration plots cover a dynamic range of four orders of magnitude, allowing for quantitative CO2 detection in various samples, like soil and breath gas. High isotopic resolution enables the excellent selectivity, sensitivity, and stability of the chosen analytical concept. The obtained isotopic resolution of typically ± 1.0 ‰ and ± 1.5 ‰ (for 3 vol. % and 0.7 vol. % of CO2, respectively) offers a promising analytical tool for isotope-ratio determination of carbon dioxide in soil gas. Preliminary experiments on soil respiration for the first time combine the on-line quantification of the overall carbon dioxide content with an optode sensor and isotopic determination (TDL system) of natural gas species.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 021
KW - Kohlendioxid
KW - Isotopenverhältnis
KW - Bodengas
KW - Diodenlaserspektroskopie
KW - tunable diode laser (TDL)
KW - carbon dioxide
KW - isotope ratios
KW - soil gas
Y1 - 2004
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-10148
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 - Löhmannsröben, Hans-Gerd
A1 - Beck, Michael
A1 - Hildebrandt, Niko
A1 - Schmälzlin, Elmar
A1 - van Dongen, Joost T.
T1 - New challenges in biophotonics : laser-based fluoroimmuno analysis and in-vivo optical oxygen monitoring
N2 - Two examples of our biophotonic research utilizing nanoparticles are presented, namely laser-based fluoroimmuno analysis and in-vivo optical oxygen monitoring. Results of the work include significantly enhanced sensitivity of a homogeneous fluorescence immunoassay and markedly improved spatial resolution of oxygen gradients in root nodules of a legume species.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 018
KW - Sauerstoff
KW - Quantenpunkt
KW - Lumineszenz
KW - Immunoassay
KW - Energietransfer
KW - Fluoreszenz-Resonanz-Energie-Transfer
KW - Nanopartikel
KW - Lanthanoide
KW - Optode
KW - Förster Resonanz Energie Transfer
KW - Biophotonik
KW - biophotonics
KW - nanoparticles
KW - immunoassay
KW - oxygen
KW - optode
Y1 - 2006
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-10120
ER -
TY - GEN
A1 - Beck, Michael
A1 - Hildebrandt, Niko
A1 - Löhmannsröben, Hans-Gerd
T1 - Quantum dots as acceptors in FRET-assays containing serum
N2 - Quantum dots (QDs) are common as luminescing markers for imaging in biological applications because their optical properties seem to be inert against their surrounding solvent. This, together with broad and strong absorption bands and intense, sharp tuneable luminescence bands, makes them interesting candidates for methods utilizing Förster Resonance Energy Transfer (FRET), e. g. for sensitive homogeneous fluoroimmunoassays (FIA). In this work we demonstrate energy transfer from Eu3+-trisbipyridin (Eu-TBP) donors to CdSe-ZnS-QD acceptors in solutions with and without serum. The QDs are commercially available CdSe-ZnS core-shell particles emitting at 655 nm (QD655). The FRET system was achieved by the binding of the streptavidin conjugated donors with the biotin conjugated acceptors. After excitation of Eu-TBP and as result of the energy transfer, the luminescence of the QD655 acceptors also showed lengthened decay times like the donors. The energy transfer efficiency, as calculated from the decay times of the bound and the unbound components, amounted to 37%. The Förster-radius, estimated from the absorption and emission bands, was ca. 77 Å. The effective binding ratio, which not only depends on the ratio of binding pairs but also on unspecific binding, was obtained from the donor emission dependent on the concentration. As serum promotes unspecific binding, the overall FRET efficiency of the assay was reduced. We conclude that QDs are good substitutes for acceptors in FRET if combined with slow decay donors like Europium. The investigation of the influence of the serum provides guidance towards improving binding properties of QD assays.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 019
KW - Quantenpunkt
KW - Lumineszenz
KW - Serum
KW - Europium
KW - Immunoassay
KW - Energietransfer
KW - Fluoreszenz-Resonanz-Energie-Transfer
KW - Förster-Resonanz-Energie-Transfer
KW - Quantum Dot
KW - Luminescence
KW - Serum
KW - Europium
KW - Immunoassay
KW - Energy Transfer
KW - FRET
Y1 - 2006
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-9504
ER -
TY - THES
A1 - Maltseva, Elena
T1 - Model membrane interactions with ions and peptides at the air/water interface
T1 - Wechselwirkungen von Modellmembranen mit Ionen und Peptiden - studiert an der Luft-Wasser-Grenzfläche
N2 - The interactions between peptides and lipids are of fundamental importance in the functioning of numerous membrane-mediated biochemical processes including antimicrobial peptide action, hormone-receptor interactions, drug bioavailability across the blood-brain barrier and viral fusion processes. Alteration of peptide structure could be a cause of many diseases. Biological membranes are complex systems, therefore simplified models may be introduced in order to understand processes occurring in nature. The lipid monolayers at the air/water interface are suitable model systems to mimic biological membranes since many parameters can be easily controlled. In the present work the lipid monolayers were used as a model membrane and their interactions with two different peptides B18 and Amyloid beta (1-40) peptide were investigated. B18 is a synthetic peptide that binds to lipid membranes that leads to the membrane fusion. It was demonstrated that it adopts different structures in the aqueous solutions and in the membrane interior. It is unstructured in solutions and forms alpha-helix at the air/water interface or in the membrane bound state. The peptide has affinity to the negatively charged lipids and even can fold into beta-sheet structure in the vicinity of charged membranes at high peptide to lipid ratio. It was elucidated that in the absence of electrostatic interactions B18 does not influence on the lipid structure, whereas it provides partial liquidization of the negatively charged lipids. The understanding of mechanism of the peptide action in model system may help to develop the new type of antimicrobial peptides as well as it can shed light on the general mechanisms of peptide/membrane binding. The other studied peptide - Amyloid beta (1-40) peptide, which is the major component of amyloid plaques found in the brain of patients with Alzheimer's disease. Normally the peptide is soluble and is not toxic. During aging or as a result of the disease it aggregates and shows a pronounced neurotoxicity. The peptide aggregation involves the conformational transition from a random coil or alpha-helix to beta-sheets. Recently it was demonstrated that the membrane can play a crucial role for the peptide aggregation and even more the peptide can cause the change in the cell membranes that leads to a neuron death. In the present studies the structure of the membrane bound Amyloid beta peptide was elucidated. It was found that the peptide adopts the beta-sheet structure at the air/water interface or being adsorbed on lipid monolayers, while it can form alpha-helical structure in the presence of the negatively charged vesicles. The difference between the monolayer system and the bulk system with vesicles is the peptide to lipid ratio. The peptide adopts the helical structure at low peptide to lipid ratio and folds into beta-sheet at high ratio. Apparently, Abeta peptide accumulation in the brain is concentration driven. Increasing concentration leads to a change in the lipid to peptide ratio that induces the beta-sheet formation. The negatively charged lipids can act as seeds in the plaque formation, the peptide accumulates on the membrane and when the peptide to lipid ratio increases it the peptide forms toxic beta-sheet containing aggregates.
N2 - Wechselwirkungen zwischen Peptiden und Lipiden sind von grundlegender Bedeutung für die Funktion vieler Membran-vermittelter biochemischer Prozesse wie der Wirkung von antimikrobiellen Peptiden, Hormon-Rezeptor Wechselwirkungen, Bioverfügbarkeit von Arzneistoffen durch die Blut-Hirn-Schranke und viraler Fusionsprozesse. Veränderungen in der Peptidstruktur können die Ursache für viele Erkrankungen sein. Biologische Membranen sind für grundlegende physikalisch-chemische Untersuchungen von Naturprozessen zu komplexe Systeme, so dass vereinfachte Modelle für solche Studien eingesetzt werden. Eine Lipidmonoschicht an der Wasser/Luft Grenzfläche ist ein geeignetes Modellsystem für eine Membranoberfläche. Viele physikalisch-chemischen Parameter können auf einfache Weise gezielt verändert werden. In der vorliegenden Arbeit wurden Lipidmonoschichten genutzt, um Wechselwirkungen mit zwei unterschiedlichen Peptiden (B18 and Amyloid Beta (1-40) Peptid) zu untersuchen. B18 ist ein oberflächenaktives synthetisches Peptid, das an Lipidmembranen bindet und zu Membranfusion führt. Es kann verschiedene Sekundärstrukturen ausbilden. So ist B18 in wässrigen Lösungen ungeordnet und bildet eine alpha-helikale Struktur an der Wasser/Luft Grenzfläche. Das Peptid hat eine große Affinität zu negativ geladenen Lipiden und kann in der Nähe von geladenen Membranoberflächen bei einem großen Peptid/Lipid Verhältnis eine Beta-Faltblatt Struktur ausbilden. Beim Fehlen elektrostatischer Wechselwirkungen hat B18 keinen Einfluss auf die Lipidstruktur. Es wirkt jedoch strukturabbauend auf anionische Lipide. Das Verständnis der Peptidwirkungen in Modellsystemen kann helfen, generelle Mechanismen von Peptide-Membran Wechselwirkungen zu verstehen und zur Entwicklung neuer antimikrobieller Peptide beizutragen. Amyloid Beta (1-40) Peptid ist die Hauptkomponente von Amyloid-Plaque, das im Gehirn von Alzheimer Patienten gefunden wird. Normalerweise ist das Peptid löslich und nicht toxisch. Hohe Neurotoxizität wird bei Peptidaggregation, die eine Strukturumwandlung von ungeordnet oder alpha-helikal zu Beta-Faltblatt nach sich zieht, beobachtet. In der vorliegenden Arbeit wurde die Struktur des Membran-gebundenen Amyloid Beta (1-40) Peptids untersucht. Es zeigte sich, dass das Peptid nach Adsorption an die Wasser/Luft Grenzfläche oder an Lipidmonoschichten eine Beta-Faltblatt Struktur ausbildet. Eine alpha-helikale Sekundärstruktur wird nur bei Anwesenheit negativ geladenen Lipidvesikel gefunden. Der entscheidende Unterschied zwischen den Monoschicht- und Vesikel-Systemen ist das Peptid/Lipid Verhältnis. Die alpha-helikale Struktur wird nur bei kleinem Peptid/Lipid Verhältnis beobachtet, während bei großem eine Beta-Faltblatt Struktur auftritt. Steigende Konzentration an Amyloid Beta (1-40) Peptid führt zum Anstieg des Peptid/Lipid Verhältnisses und damit zur Ausbildung der Beta-Faltblatt Struktur. Negativ geladene Lipide können somit als Keimpunkte für die Plaquebildung fungieren.
KW - Lipide
KW - Monoschicht
KW - Peptide
KW - Phospholipid
KW - Langmuir monolayers
KW - IRRAS
KW - Amyloid peptide
Y1 - 2005
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-5670
ER -