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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.
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.
For the first time stabilizer-free vinylidene fluoride (VDF) polymerizations were carried out in homogeneous phase with supercritical CO₂. Polymerizations were carried out at 140°C, 1500 bar and were initiated with di-tert-butyl peroxide (DTBP). In-line FT-NIR (Fourier Transform- Near Infrared) spectroscopy showed that complete monomer conversion may be obtained. Molecular weights were determined via size-exclusion chromatography (SEC) and polymer end group analysis by 1H-NMR spectroscopy. The number average molecular weights were below 104 g∙mol−1 and polydispersities ranged from 3.1 to 5.7 depending on DTBP and VDF concentration. To allow for isothermal reactions high CO₂ contents ranging from 61 to 83 wt.% were used. The high-temperature, high-pressure conditions were required for homogeneous phase polymerization. These conditions did not alter the amount of defects in VDF chaining. Scanning electron microscopy (SEM) indicated that regular stack-type particles were obtained upon expansion of the homogeneous polymerization mixture. To reduce the required amount of initiator, further VDF polymerizations using chain transfer agents (CTAs) to control molecular weights were carried out in homogeneous phase with supercritical carbon dioxide (scCO₂) at 120 °C and 1500 bar. Using perfluorinated hexyl iodide as CTA, polymers of low polydispersity ranging from 1.5 to 1.2 at the highest iodide concentration of 0.25 mol·L-1 were obtained. Electrospray ionization- mass spectroscopy (ESI-MS) indicates the absence of initiator derived end groups, supporting livingness of the system. The “livingness” is based on the labile C-I bond. However, due to the weakness of the C-I bond perfluorinated hexyl iodide also contributes to initiation. To allow for kinetic analyses of VDF polymerizations the CTA should not contribute to initiation. Therefore, additional CTAs were applied: BrCCl3, C6F13Br and C6F13H. It was found that C6F13H does not contribute to initiation. At 120°C and 1500 bar kp/kt0.5~ 0.64 (L·mol−1·s−1)0.5 was derived. The chain transfer constant (CT) at 120°C has been determined to be 8·10−1, 9·10−2 and 2·10−4 for C6F13I, C6F13Br and C6F13H, respectively. These CT values are associated with the bond energy of the C-X bond. Moreover, the labile C-I bond allows for functionalization of the polymer to triazole end groups applying click reactions. After substitution of the iodide end group by an azide group 1,3 dipolar cycloadditions with alkynes yield polymers with 1,2,3 triazole end groups. Using symmetrical alkynes the reactions may be carried out in the absence of any catalyst. This end-functionalized poly (vinylidene fluoride) (PVDF) has higher thermal stability as compared to the normal PVDF. PVDF samples from homogeneous phase polymerizations in supercritical CO₂ and subsequent expansion to ambient conditions were analyzed with respect to polymer end groups, crystallinity, type of polymorphs and morphology. Upon expansion the polymer was obtained as white powder. Scanning electron microscopy (SEM) showed that DTBP derived polymer end groups led to stack-type particles whereas sponge- or rose-type particles were obtained in case of CTA fragments as end groups. Fourier-Transform Infrared spectroscopy and wide angle X-ray diffraction indicated that the type of polymorph, α or β crystal phase was significantly affected by the type of end group. The content of β-phase material, which is responsible for piezoelectricity of PVDF, is the highest for polymer with DTBP-derived end groups. In addition, the crystallinity of the material, as determined via differential scanning calorimetry is affected by the end groups and polymer molecular weights. For example, crystallinity ranges from around 26 % for DTBP-derived end groups to a maximum of 62 % for end groups originating from perfluorinated hexyl iodide for polymers with Mn ~2200 g·mol–1. Expansion of the homogeneous polymerization mixture results in particle formation by a non-optimized RESS (Rapid Expansion from Supercritical Solution) process. Thus, it was tested how polymer end groups affect the particles size distribution obtained from RESS process under controlled conditions (T = 50°C and P = 200 bar). In all RESS experiments, small primary PVDF with diameters less than 100 nm without the use of liquid solvents, surfactants, or other additives were produced. A strong correlation between particle size and particle size distribution with polymer end groups and molecular weight of the original material was observed. The smallest particles were found for RESS of PVDF with Mn~ 4000 g·mol–1 and PFHI (C6F13I) - derived end groups.
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.
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.
Aus dem Inhalt: Die Juvenilhormone 1a-c werden im Blut von Insekten enzymatisch zu den biologisch inaktiven Sluren hydrolysiert. Bei der Hydrolyse von racemischem 1c im Blut der Wanderheuschrecke Locusta migratoria wird ein Umsatz von 40-60% erreicht. Das unumgesetzte Edukt enthällt einen Überschuß an natürlich konfiguriertem (10R)-1c (e.e. 47.2%). Wir konnten zeigen, daß das in der Hämolymphe vorhandene Hormon-Bindungsprotein bevorzugt mit (10R)- 1c assoziiert.
The synthesis of galactose clusters that are linked to a steroid moiety by a peptide-like spacer unit is described. The galactose cluster is obtained by Koenigs-Knorr glycosylation of TRIS-Gly-Fmoc (2b) under Helferich conditions. Peptide and ester bonds are formed after activation of carboxylic acids as diphenylthiophene dioxide (TDO) esters. 6a is synthesized in a convergent way by coupling of (Ac4Gal)3-TRIS-Gly (3e) with cholesteryl TDO succinate (5b). Coupling of (Ac4Gal)3-TRIS-Gly hydrogen succinate (3f) with Gly-O-Chol (5d) by means of EEDQ yields 6d. Reaction of (Ac4Gal)3-TRIS-Gly-SUCC-O-TDO (3g) with 25-hydroxycholesterol leads in a linear sequence to the oxysterol derivative 6f. Selective cleavage of the acetyl groups from galactose units yields the known compound 6b and the new derivatives 6e and 6g.
Die Arbeit beschreibt die Synthese, Charakterisierung und Anwendung von meso- und mikroporösen Hochleistungspolymeren. Im ersten Teil wird die Synthese von mesoporösen Polybenzimidazol (PBI) auf der Basis einer Templatierungsmethode vorgestellt. Auf der Grundlage kommerzieller Monomere und Silikatnanopartikel sowie eines neuen Vernetzers wurde ein Polymer-Silikat-Hybridmaterial aufgebaut. Das Herauslösen des Silikats mit Ammoniumhydrogendifluorid führt zu mesoporösen Polybenzimidazolen mit spherischen Poren von 9 bis 11 nm Durchmesser. Die Abhängigkeit der beobachteten Porosität vom Massenverhältnis Silikat zu Polymer wurde ebenso untersucht wie die Abhängigkeit der Porosität vom Vernetzergehalt. Die Porosität vollvernetzter Proben zeigt eine lineare Abhängigkeit vom Verhältnis Silikat zu Polymer bis zu einem Grenzwert von 1. Wird der Grenzwert überschritten, ist teilweiser Porenkollaps zu beobachten. Die Abhängigkeit der Porosität vom Vernetzergehalt bei festem Silikatgehalt ist nichtlinear. Oberhalb einer kritischen Vernetzerkonzentration wird eine komplette Replikation der Nanopartikel gefunden. Ist die Vernetzerkonzentration dagegen kleiner als der kritische Wert, so ist der völlige Kollaps einiger Poren bei Stabilität der verbleibenden Poren zu beobachten. Ein komplett unporöses PBI resultiert bei Abwesenheit des Vernetzers. Die mesoporösen PBI-Netzwerke konnten kontrolliert mit Phosphorsäure beladen werden. Die erhaltenen Addukte wurden auf ihre Protonenleitfähigkeit untersucht. Es kann gezeigt werden, dass die Nutzung der vordefinierten Morphologie im Vergleich zu einem unstrukturierten PBI in höheren Leitfähigkeiten resultiert. Durch die vernetzte Struktur war des Weiteren genügend mechanische Stabilität gegeben, um die Addukte reversibel und bei sehr guten Leitfähigkeiten bis zu Temperaturen von 190°C bei 0% relativer Feuchtigkeit zu untersuchen. Dies ist für unstrukturierte Phosphorsäure/PBI - Addukte aus linearem PBI nicht möglich. Im zweiten Teil der Arbeit wird die Synthese intrinsisch mikroporöser Polyamide und Polyimide vorgestellt. Das Konzept intrinsisch mikroporöser Polymere konnte damit auf weitere Polymerklassen ausgeweitet werden. Als zentrales, strukturinduzierendes Motiv wurde 9,9'-Spirobifluoren gewählt. Dieses Molekül ist leicht und vielfältig zu di- bzw. tetrafunktionellen Monomeren modifizierbar. Dabei wurden bestehende Synthesevorschriften modifiziert bzw. neue Vorschriften entwickelt. Ein erster Schwerpunkt innerhalb des Kapitels lag in der Synthese und Charakterisierung von löslichen, intrinsisch mikroporösen, aromatischen Polyamid und Polyimid. Es konnte gezeigt werden, dass das Beobachten von Mikroporosität stark von der molekularen Architektur und der Verarbeitung der Polymere abhängig ist. Die Charakterisierung der Porosität erfolgte unter Nutzung von Stickstoffsorption, Kleinwinkelröntgenstreuung und Molecular Modeling. Es konnte gezeigt werden, dass die Proben stark vom Umgebungsdruck abhängigen Deformationen unterliegen. Die starke Quellung der Proben während des Sorptionsvorgangs konnte durch Anwendung des "dual sorption" Modells, also dem Auftreten von Porenfüllung und dadurch induzierter Henry-Sorption, erklärt werden. Der zweite Schwerpunkt des Kapitels beschreibt die Synthese und Charakterisierung mikroporöser Polyamid- und Polyimidnetzwerke. Während Polyimidnetzwerke auf Spirobifluorenbasis ausgeprägte Mikroporosität und spezifische Oberflächen von ca. 1100 m²/g aufwiesen, war die Situation für entsprechende Polyamidnetzwerke abweichend. Mittels Stickstoffsorption konnte keine Mikroporosität nachgewiesen werden, jedoch konnte mittels SAXS eine innere Grenzfläche von ca. 300 m²/g nachgewiesen werden. Durch die in dieser Arbeit gezeigten Experimente kann die Grenze zwischen Polymeren mit hohem freien Volumen und mikroporösen Polymeren somit etwas genauer gezogen werden. ausgeprägte Mikroporosität kann nur in extrem steifen Strukturen nachgewiesen werden. Die Kombination der Konzepte "Mesoporosität durch Templatierung" und "Mikroporosität durch strukturierte Monomere" hatte ein hierarchisch strukturiertes Polybenzimidazol zum Ergebnis. Die Präsenz einer Strukturierung im molekularen Maßstab konnte SAXS bewiesen werden. Das so strukturierte Polybenzimidazol zeichnete sich durch eine höhere Protonenleitfähigkeit im Vergleich zu einem rein mesoporösen PBI aus. Der letzte Teil der Arbeit beschäftigte sich mit der Entwicklung einer neuen Synthesemethode zur Herstellung von Polybenzimidazol. Es konnte gezeigt werden, dass lineares PBI in einer eutektischen Salzschmelze aus Lithium- und Kaliumchlorid synthetisiert werden kann. Die Umsetzung der spirobifluorenbasierten Monomere zu löslichem oder vernetztem PBI ist in der Salzschmelze möglich.
The aim of this work was the generation of carbon materials with high surface area, exhibiting a hierarchical pore system in the macro- and mesorange. Such a pore system facilitates the transport through the material and enhances the interaction with the carbon matrix (macropores are pores with diameters > 50 nm, mesopores between 2 – 50 nm). Thereto, new strategies for the synthesis of novel carbon materials with designed porosity were developed that are in particular useful for the storage of energy. Besides the porosity, it is the graphene structure itself that determines the properties of a carbon material. Non-graphitic carbon materials usually exhibit a quite large degree of disorder with many defects in the graphene structure, and thus exhibit inherent microporosity (d < 2nm). These pores are traps and oppose reversible interaction with the carbon matrix. Furthermore they reduce the stability and conductivity of the carbon material, which was undesired for the proposed applications. As one part of this work, the graphene structures of different non-graphitic carbon materials were studied in detail using a novel wide-angle x-ray scattering model that allowed precise information about the nature of the carbon building units (graphene stacks). Different carbon precursors were evaluated regarding their potential use for the synthesis shown in this work, whereas mesophase pitch proved to be advantageous when a less disordered carbon microstructure is desired. By using mesophase pitch as carbon precursor, two templating strategies were developed using the nanocasting approach. The synthesized (monolithic) materials combined for the first time the advantages of a hierarchical interconnected pore system in the macro- and mesorange with the advantages of mesophase pitch as carbon precursor. In the first case, hierarchical macro- / mesoporous carbon monoliths were synthesized by replication of hard (silica) templates. Thus, a suitable synthesis procedure was developed that allowed the infiltration of the template with the hardly soluble carbon precursor. In the second case, hierarchical macro- / mesoporous carbon materials were synthesized by a novel soft-templating technique, taking advantage of the phase separation (spinodal decomposition) between mesophase pitch and polystyrene. The synthesis also allowed the generation of monolithic samples and incorporation of functional nanoparticles into the material. The synthesized materials showed excellent properties as an anode material in lithium batteries and support material for supercapacitors.
Im vorliegenden Beitrag wird an Hand dreier Beispiele der Einsatz von optischer Sensorik zur Produktcharakterisierung dargestellt, nämlich Untersuchungen zum O2-Gehalt in Fruchtsäften, zur Isotopiesignatur von CO2 in Mineralwässern und zu Lichtstreueigenschaften eines Sonnenschutzmittels. Inhalt: Bestimmung von O2 mit Lumineszenzsonden Isotopenselektive Bestimmung von CO2 mit TDLAS Optische Charakterisierung stark streuender Materialien mit Photonendichtewellen