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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

EPR studium radikálových reakcí sekundárních aminů probíhajících v kapalné fázi / EPR Study of Radical Reactions of Secondary Amines in Liquid Phase

Šafaříková, Lenka January 2014 (has links)
In the framework of Ph.D. thesis the evaluation of radical reactions of four groups of secondary amines R1–NH–R2 in the presence of some selected types of agents was performed using EPR spectroscopy. First group was represented by peroxoagents (3-chloroperbenzoic acid, tBuO2 radicals), the second group involved compounds of PbIV+ (PbO2, Pb(OAc)4) functioning as hydrogen-abstracting agents. In the presence of peroxyagents the formation of corresponding aminoxyl radicals R1–NO–R2 was demonstrated. In the case of surplus of tBuO2 radicals these radicals enter the consecutive reactions which products are new types of secondary aminoxyls. By the interpretation of reaction mechanism the intermediary formation of nitrones was assumed. These function in later steps of the reaction as spin traps for tBuO2 radicals. By the study of radical mechanism of amines R1–NH–R2 initiated by PbIV+ agents was proved, that these compounds hydrogen atom not only from –NH– group under formation of aminyl radicals, but also from C–H bonds in substituents R1, R2 (the formation of C-radicals). Because both groups of the radicals formed are characterized by high reactivity, their identification was possible only using spin-trapping method. In the course of the investigation of radical reactions of secondary amines the big amount of experimental EPR spectra was obtained. These exhibited in many cases very high hyperfine structure. Due to this fact it was necessary to perform the detailed evaluation on the basis of spectral simulation. Except of some special cases using this approach the interpretation of majority of registered EPR spectra was interpreted and EPR parameters were summarized in tables.
2

Quantitative Electron Paramagnetic Resonance Studies of Charge Transfer in Organic Semiconductors / Quantitative Elektron Paramagnetische Resonanz Untersuchungen von Ladungstransfer Prozessen in Organischen Halbleitern

Auth, Michael Tilman January 2020 (has links) (PDF)
In the present work we investigated various charge transfer processes, as they appear in the versatile world of organic semiconductors by probing the spin states of the corresponding charge carrier species via electron paramagnetic resonance (EPR) spectroscopy. All studied material systems are carbon-based compounds, either belonging to the group of polymers, fullerenes, or single-wall carbon nanotubes (SWNTs). In the first instance, we addressed the change of the open circuit voltage (Voc) with the fullerene blend stoichiometry in fullerene-based solar cells for organic photovoltaics (OPV). The voltage depends strongly on the energy separation between the lowest unoccupied molecular orbital (LUMO) of the donor and the highest occupied molecular orbital (HOMO) of the acceptor. By exploiting the Gaussian distribution of the charge carriers in a two-level system, and thus also their spins in the EPR experiment, it could be shown that the LUMOs get closer by a few to a few hundred meV when going from pure fullerene materials to a fullerene mixture. The reason for this strong energetic effect is likely the formation of a fullerene alloy. Further, we investigated the chemical doping mechanism of SWNTs with a (6,5)-chirality and their behaviour under optical excitation. In order to determine the unintentional (pre)-doping of SWNTs, EPR spectra of the raw material as well as after different purification steps were recorded. This facilitated the determination of nanotube defects and atmospheric p-doping as the causes of the measured EPR signals. In order to deliberately transfer additional charge carriers to the nanotubes, we added the redox-active substance AuCl3 where we determined an associated doping-yield of (1.5±0.2)%. In addition, a statistical occupation model was developed which can be used to simulate the distribution of EPR active, i.e. unpaired and localised charge carriers on the nanotubes. Finally, we investigated the charge transfer behaviour of (6,5)-SWNTs together with the polymer P3HT and the fullerene PC60BM after optical excitation. / Die vorliegende Arbeit untersuchte mit Hilfe der Elektron Paramagnetischen Resonanz Spektroskopie (EPR) die Ladungsträgerspins bei Ladungstransfer-Prozessen in organischen Halbleitern. Insbesondere wurden hier verschiedene Kohlenstoffverbindungen betrachtet, welche zur Gruppe der Polymere, Fullerene, oder Kohlenstoff-Nanoröhren gehören. Zu Beginn gingen wir auf die Veränderung der Leerlaufspannung in Fulleren Solarzellen für organische photovoltaic (OPV) ein, welche mit der Fulleren Stöchiometry variiert. Die Leerlaufspannung ist entscheidend für das Ladungsstransfer-Verhalten nach erfolgreicher optischer Anregung. Sie hängt stark vom Energieabstand des niedrigsten unbesetzten Molekülorbitals (engl. LUMO) des Donators zum höchsten besetzten Molekülorbital (engl. HOMO) des Akzeptors ab. Hierbei wurde die Gaußsche Verteilungs-Statistik der Ladungsträger, und damit auch deren Spins, in einem zwei Niveau System im EPR Experiment ausgenutzt. Es konnte gezeigt werden, dass sich deren Abstand um wenige bis hin zu wenigen Hundert meV annähert wenn man vom reinen Fulleren Material zu einem Fulleren Gemisch übergeht. Die Ursache für diesen starken energetischen Effekt ist wahrscheinlich die Bildung einer Fulleren-Legierung. Des weiteren betrachteten wir speziell einwandige Kohlenstoff-Nanoröhren der Chiralität (6,5). Untersucht wurde zunächst die chemische Dotierung dieser Systeme und anschließend ihr Verhalten bei optischer Anregung. Um zunächst die ungewünschte (vor)-Dotierung der Nanoröhren zu ermitteln, wurden EPR Spektren in unbehandelter Form, als auch nach unterschiedlichen Aufreinigungsschritten aufgenommen. Dies ermöglichte die Bestimmung von Nanorohr-Defekten und atmosphärischer p-Dotierung als Ursache für das gemessene EPR Signal. Um bewusst zusätzliche Ladungsträger auf die Nanoröhren zu übertragen gaben wir die redox-aktive Substanz AuCl3 hinzu, wo wir eine zugehörige Dotiereffizienz von (1,5±0,2)% ermittelten. Darüber hinaus wurde ein statistisches Modell erarbeitet welches die Verteilung von EPR aktiven, d.h. ungepaarten und lokalisierten Ladungsträgern auf den Nanoröhren simulieren kann. Zum Abschluss betrachteten wir das Ladungstransfer-Verhalten von (6,5)-Nanoröhren zusammen mit dem Polymer P3HT und dem Fulleren PC60BM nach optischer Anregung.
3

EPR studium radikálových reakcí, iniciovaných rozpadem vybraných typů peroxidických sloučenin / EPR study of radical reactions initiated by the decomposition of selected types of peroxy compounds

Krkošková, Petra January 2010 (has links)
The products of the decomposition of selected types of peroxo compounds in the presence of redox agents (Pb and Co compounds) were investigated by EPR method. Besides some commercial peroxides the study was performed with peroxo compounds of Luperoxide group (Luperox 101, Luperox 256, Luperox 531). For the detection of the decomposition products the technique of spin-trapping using nitrosobenzene was applied. EPR spectra of radical adducts formed by the reaction of the reactive oxygenous radicals with nitrosobenzen having the character of stable nitroxyl radicals were analyzed. Their EPR parameters were obtained by simulation method. Besides the addition to nitrosobenzene the generated oxygen centered radicals were proved also on the basis of their reaction with model compounds (Santonox R; 2,6–ditercbutyl–4–methylphenol; diphenylamine).
4

Cw and pulsed EPR spectroscopy of Cu(II) and V(IV) in metal-organic framework compounds: metal ion coordination and adsorbate interactions

Jee, Bettina 24 October 2013 (has links) (PDF)
Metal-organic framework (MOF) compounds as a new class of porous coordination polymers consists of metal ions or clusters linked by organic molecules. They have gained recent interest because of their large surface areas and huge variety of the porous network structures. They exhibit interesting adsorption properties and therefore are potential candidates for various technical applications. In this work, continuous wave (cw) and pulsed electron paramagnetic resonance (EPR) methods such as pulsed electron-nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopy are applied to study metal-organic frameworks with respect to different aspects of their properties: The host-guest interactions between Cu2+ ions in [Cu3(btc)2]n (HKUST-1; btc: 1,3,5-benzenetricaboxylate) with adsorbed methanol (CH3OH), 13C enriched carbon monoxide and dioxide (13CO, 13CO2), hydrogen (H2), deuterium (D2) and mixed isotopic HD. In [Cu3(btc)2]n, the Cu2+ ions are connected to binuclear Cu/Cu paddle wheel units. Since the Cu2+ ions in the [Cu3(btc)2]n are antiferromagnetically coupled, the new compound [Cu2.97Zn0.03(btc)2]n is synthesized by isomorphous substitution containing about 1 % paramagnetic Cu/Zn paddle wheel units. The modified Cu/Zn paddle wheel units prove to be a very sensitive probe for the interactions with the adsorbed molecules. Secondly, the exchange interactions of antiferromagnetically coupled Cu/Cu paddle wheel units as well as additional inter-paddle wheel exchange interactions between the Cu/Cu pairs are studied in [Cu2(bdc)2(dabco)]n, a layered MOF with 1,4-benzenedicaboxylate (bdc) as linker and 1,4-diazabicyclo[2.2.2]octane (dabco) acting as pillars between the layers. In comparison to [Cu3(btc)2]n, the additional inter-paddle wheel exchange interactions are much easier disturbed by incorporation of Zn2+ ions into the framework structure. Third, the structural dynamics of the framework is investigated in the compound [Al(OH)(bdc)]n (MIL-53) which was isomorphously substituted by V(III)/V(IV) species. The 51V hyperfine structure revealed to be sensitive to the so-called breathing effect, a flexible structural behaviour upon guest adsorption/desorption or upon thermal treatment. It is shown that the aluminum ions can be substituted by vanadium but the octahedral coordination environment changes slightly to a pseudo-octahedral or a square-pyramidal coordination. Based on the hyperfine interactions between the electron spin and the nuclear spins of the surrounding atoms, structural models can be derived from orientation-selective measurements. In such a way, structural information of materials like powder samples and adsorbate complexes can be obtained which are hardly or even not accessible by other methods.
5

Charakterizace plodů aronie (Aronia melanocarpa) a muchovníku (Amelanchier alnifolia) / Characterisation of chokeberry and saskatoon berry fruits

Burdějová, Lenka January 2014 (has links)
Diploma thesis deals with the characterization of chokeberry (Aronia melanocarpa) and saskatoon berry (Amelanchier alnifolia) fruits. The theoretical part focuses on the botanical classification, chemical composition, curative effects and the use of chokeberry and saskatoon berry in the food industry. Further, the attention is also devoted to a review of methods for the determination of important antioxidants, specialized on the determination of polyphenols, anthocyanins, ascorbic acid and total antioxidant activity. The experimental part of the work deals with the determination of selected parameters in different varieties of chokeberry and serviceberry, harvested in 2012 and 2013 using spectroscopic and chromatographic techniques with an emphasis on effect of solvent (50% ethanol, destilled water, DMSO). Specifically total content of polyphenols and anthocyanins, color characteristics using the CIE L*a*b* system and the ability of the sample to reduce the iron are determined using the UV-VIS-NIR spectroscopy. Further ascorbic acid concentration in individual extracts is quantified by High performance liquid chromatography coupled with a diode array detector and the total antioxidant activity is characterized by electron paramagnetic resonance involving •DPPH and ABTS•+ assays.
6

Radikálové reakce rozpadu N-H, O-H a O-O vazeb účinkem homogenních a heterogenních redox činidel. / Radical Reactions of the Decomposition of N-H, O-H and O-O Bonds Initiated by Homogeneous and Heterogeneous Redox Agents

Majzlík, Petr January 2010 (has links)
The Ph.D. thesis was focused on EPR study of redox reactions of selected types of phenols, secondary amines and diperoxy coumpounds. Within the study some redox agents were employed in nonpolar, in some special cases also in polar solvents. EPR spectra of generated radical products were interpreted using spectral simulation. Study of radical reactions under participation of phenols was preferentially concentrated on the behavior of para methyl substituted phenols, where the instability of this substituent in relation to the applied redox agents was evaluated. The tendency towards the abstraction of hydrogen from methyl group, representing the paralell mechanism to the hydrogen abstaction from phenolic OH group was proved. The generated benzyl radicals were undirectly detected in the form of adducts with aromatic nitroso compounds. These adducts undergo the consecutive transformations, leading to the formation of new types of phenoxy radicals. The study of the decomposition of NH bonds was performed with substituted N,N´-paraphenylenediamines, 1-anilino-1-phenylpentane-3-ones and amino substituted 1,3-dimethyluracils. By the oxidation with 3-chloroperbenzoic acid the corresponding nitroxyl radicals were prepared. In the case of 1-anilino-1-phenylpentane-3-ones the aminyl radicals were prepared by the oxidation with PbO2, which existence was evidenced by spin trapping method with nitrosobenzene. In the framework of the investigation of the decomposition of -O-O- bonds the oxygen centred radicals, generated from peroxidic compounds of Luperox type using selected redox agents were detected by spin trapping method. The analysis of EPR spectra documented that primary alkoxyl radicals undergo the consecutive fragmentation, which leads in the presence of oxygen to the formation of secondary alkoxyl radicals. The generation of oxygen centred radicals during the decomposition was indirectly proved in the presence of model phenolic compounds, where due to the abstraction of hydrogen from phenolic OH group the phenoxyl radicals are formed.
7

Cw and pulsed EPR spectroscopy of Cu(II) and V(IV) in metal-organic framework compounds: metal ion coordination and adsorbate interactions

Jee, Bettina 25 September 2013 (has links)
Metal-organic framework (MOF) compounds as a new class of porous coordination polymers consists of metal ions or clusters linked by organic molecules. They have gained recent interest because of their large surface areas and huge variety of the porous network structures. They exhibit interesting adsorption properties and therefore are potential candidates for various technical applications. In this work, continuous wave (cw) and pulsed electron paramagnetic resonance (EPR) methods such as pulsed electron-nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopy are applied to study metal-organic frameworks with respect to different aspects of their properties: The host-guest interactions between Cu2+ ions in [Cu3(btc)2]n (HKUST-1; btc: 1,3,5-benzenetricaboxylate) with adsorbed methanol (CH3OH), 13C enriched carbon monoxide and dioxide (13CO, 13CO2), hydrogen (H2), deuterium (D2) and mixed isotopic HD. In [Cu3(btc)2]n, the Cu2+ ions are connected to binuclear Cu/Cu paddle wheel units. Since the Cu2+ ions in the [Cu3(btc)2]n are antiferromagnetically coupled, the new compound [Cu2.97Zn0.03(btc)2]n is synthesized by isomorphous substitution containing about 1 % paramagnetic Cu/Zn paddle wheel units. The modified Cu/Zn paddle wheel units prove to be a very sensitive probe for the interactions with the adsorbed molecules. Secondly, the exchange interactions of antiferromagnetically coupled Cu/Cu paddle wheel units as well as additional inter-paddle wheel exchange interactions between the Cu/Cu pairs are studied in [Cu2(bdc)2(dabco)]n, a layered MOF with 1,4-benzenedicaboxylate (bdc) as linker and 1,4-diazabicyclo[2.2.2]octane (dabco) acting as pillars between the layers. In comparison to [Cu3(btc)2]n, the additional inter-paddle wheel exchange interactions are much easier disturbed by incorporation of Zn2+ ions into the framework structure. Third, the structural dynamics of the framework is investigated in the compound [Al(OH)(bdc)]n (MIL-53) which was isomorphously substituted by V(III)/V(IV) species. The 51V hyperfine structure revealed to be sensitive to the so-called breathing effect, a flexible structural behaviour upon guest adsorption/desorption or upon thermal treatment. It is shown that the aluminum ions can be substituted by vanadium but the octahedral coordination environment changes slightly to a pseudo-octahedral or a square-pyramidal coordination. Based on the hyperfine interactions between the electron spin and the nuclear spins of the surrounding atoms, structural models can be derived from orientation-selective measurements. In such a way, structural information of materials like powder samples and adsorbate complexes can be obtained which are hardly or even not accessible by other methods.:1 Introduction 1.1 Electron paramagnetic resonance spectroscopy for investigation of porous materials 1.2 Metal-organic frameworks 1.3 Implementation of paramagnetism by isomorphous substitution 1.4 EPR spectroscopic methods 1.4.1 Spin Hamiltonian 1.4.2 cw EPR spectroscopy 1.4.3 Pulsed EPR spectroscopy 1.5 Description of the project 2 [Cu2.97Zn0.03(btc)2]n 2.1 Introduction: Monometallic [Cu3(btc)2]n (1) 2.1.1 Spin coupling 2.1.2 Adsorption of H2O 2.1.3 Adsorption of DTBN 2.2 Isomorphous substitution of Cu2+ by Zn2+ in [Cu3(btc)2]n 2.2.1 Synthesis and characterisation of [Cu2.97Zn0.03(btc)2]n (2) 2.2.2 cw EPR spectroscopy of 2 2.2.3 Pulsed EPR spectroscopy of 2 2.2.4 Summary: Zn2+ substitution 2.3 Adsorption of methanol (MeOH) on [Cu2.97Zn0.03(btc)2]n (2_MeOH) 2.3.1 cw EPR spectroscopy of 2_MeOH 2.3.2 Pulsed EPR spectroscopy of 2_MeOH 2.3.3 Discussion 2.3.4 Summary: adsorption of MeOH 2.4 Adsorption of 13CO2 and 13CO on [Cu2.97Zn0.03(btc)2]n (2_CO2, 2_CO) 2.4.1 cw EPR spectroscopy of 2_CO2 and 2_CO 2.4.2 Pulsed EPR spectroscopy of 2_CO2 and 2_CO 2.4.3 Discussion 2.4.4 Summary: adsorption of 13CO2 and 13CO 2.5 Adsorption of H2, D2 and HD on [Cu2.97Zn0.03(btc)2]n (2_HH, 2_DD and 2_HD) 2.5.1 cw EPR spectroscopy of 2_HH, 2_DD and 2_HD 2.5.2 Pulsed EPR spectroscopy of 2_HH, 2_DD and 2_HD 2.5.2.1 3p ESEEM spectroscopy of 2_HH, 2_DD and 2_HD 2.5.2.2 Davies-ENDOR spectroscopy of 2_HH 2.5.2.3 Davies-ENDOR spectroscopy of 2_HD 2.5.2.4 Davies-ENDOR spectroscopy of 2_DD 2.5.3 Discussion 2.5.4 Summary: adsorption of H2, D2 and HD 2.6 Conclusion: [Cu2.97Zn0.03(btc)2]n 3 [Cu2(bdc)2(dabco)]n (3) and [Cu(2-x)Zn(x)(bdc)2(dabco)]n (3_x) 3.1 [Cu2(bdc)2(dabco)]n (3) 3.2 [Cu1.9Zn0.1(bdc)2(dabco)]n (3_0.1) 3.3 [Cu(2-x)Zn(x)(bdc)2(dabco)]n (3_0.5, 3_1.0, 3_1.5 and 3_1.9) 3.4 Determination of the exchange coupling constant J 3.5 Discussion 3.6 Conclusions: [Cu(2-x)Zn(x)(bdc)2(dabco)]n (3_x) 4 [(AlOH)1-x(VO)x(bdc)]n (4) and [(AlOH)1-x(VO)x(ndc)]n (5) 4.1 Introduction 4.2 EPR spectroscopic investigations of mixed-metal bdc compounds 4.3 EPR spectroscopic investigations of mixed-metal ndc compounds 4.4: Conclucions: V(III)/V(IV) substitution in [Al(OH)(bdc)]n and [Al(OH)(ndc)]n 5 Summary and Conclusion 5.1 Host-guest interactions 5.2 Exchange couplings of Cu/Cu pairs 5.3 Structural dynamics of the bdc and the ndc framework 5.4 Conclusion 6 Appendix 6.1 Experimental details and additional spectra 6.2 Instrumental details 6.3 Curriculum vitae and publications
8

Studies on the late rhodopsin activation steps

Knierim, Bernhard 20 March 2008 (has links)
Rhodopsin ist der Photorezeptor der Stäbchenzellen in der Retina von Vertebraten und wird als Prototyp für die gesamte Gruppe der GPCRs beforscht. Trifft ein Photon auf das Protein, so wird der über eine Schiffbase kovalent gebundene Chromophor von seiner 11-cis- in die All-trans-Konfiguration isomerisiert und setzt infolgedessen den Aktivierungsprozess in Gang. Dieser mündet in der aktiven Rezeptorkonformation, die das G-Protein Transducin aktivieren kann und dadurch eine Kaskade weiterer Aktivierungsschritten einleitet, die letztlich ein Nervensignal verursachen. Das Ziel dieser Arbeit war die Aufklärung der späten Aktivierungsschritte und ihrer Ursache-Wirkungs-Beziehungen. Zu diesem Zweck wurden Blitzlichtphotolyse, Elektronenspinresonanz (EPR) mit Spinlabeling (SDSL), UV/vis-Spektroskopie, FTIR-Spektroskopie und Fluoreszenzspektroskopie angewandt. Kinetische Messungen wurden unter identischen Bedingungen durchgeführt, um die Abfolge der mit den unterschiedlichen Techniken zugänglichen Aktivierungsschritte aufzuklären. Nach der Bildung des absorptionsspektroskopisch definierten Meta-II-Zustands bewegt sich die Helix TM6 in einem späteren Schritt als ganzes nach außen und markiert damit den Übergang von Meta-IIa zu Meta-IIb. Dadurch wird die bis dahin in der Membran verborgene D(E)RY-Region für das Umgebungsmedium zugänglich und nimmt ohne Zeitverzögerung ein Proton auf, wodurch der Meta-IIb*H+-Zustand gebildet wird. Die verfügbaren Daten sprechen dafür, dass das D(E)RY-Motiv bei der Aktivierung des Transducins sowohl die Alpha- als auch die Gamma-Untereinheit desselben bindet. Die Bindung von zu Transducin-Abschnitten analogen Peptiden kann dann erfolgen, wenn die Helix TM6 im nach außen bewegten Zustand ist, und führt zur Abgabe von bis zu zwei Protonen vom aktivierten Rhodopsin. Sowohl das D(E)RY- und das NPxxY(x)5,6F-Motiv als auch die beiden Zustände Meta-IIb und Meta-IIb*H+ könnten relevant für den sequenziellen Transducin-Aktivierungsmechanismus sein. / Rhodopsin is the photoreceptor in the rod cells of the vertebrate retina. It is considered as a prototype of the whole group of GPCRs. Upon absorption of a photon the chromophore, which is covalently bound through a Schiff base, is isomerized from its 11-cis into the all-trans configuration. This initiates the activation process and finally results in the active receptor conformation which is capable of activating the G protein transducin and thereby triggers a cascade of further activation steps which finally cause a nerve signal. The aim of this work was the clarification of the late activation steps and their cause-and-effect chain. For this purpose flash photolysis, electron paramagnetic resonance (EPR) with spin labeling (SDSL), UV/vis spectroscopy, FTIR spectroscopy and fluorescence spectroscopy were applied. Kinetic measurements were executed under identical conditions in order to elucidate the sequence of activation steps, which are accessible with the different techniques. After formation of the spectroscopically defined Meta-II state helix TM6 moves outward as a rigid body, thereby marking the transition from Meta-IIa to Meta-IIb. Therefore the D(E)RY region, which is until then buried in the membrane, gets accessible to the surrounding solution. It consequently takes up a proton without delay, thus forming the Meta-IIb*H+ state. Available data argue for the D(E)RY motif binding both the Alpha and the Gamma subunit of transducin during activation of the latter. The binding of peptides which are analogous to sections of transducin is possible when helix TM6 is in the outward position. It causes the release of up to two protons from the activated rhodopsin. Both the D(E)RY motif and the NPxxY(x)5,6F motif as well as both the states Meta-IIb and Meta-IIb*H+ are potentially relevant for the sequential transducin activation mechanism.
9

Untersuchungen zum „Controlled SBU Approach“ an metall-organischen Gerüstverbindungen und Syntheseversuche metallsubstituierter MOF-5- und MOF-177-Homologer / Investigation of the „Controlled SBU Approach“ of metal-organic frameworks and synthesis of metal substituted IRMOF- and MOF-177-homologues

Müller, Tobias 05 July 2012 (has links) (PDF)
Die potentiellen Precursor Magnesiumoxobromid bzw. Mangan(II,III)-oxopivalat für die noch unbekannten metallsubstituierten IRMOF-Homologen MOF-5(Mg) bzw. MOF-5(Mn) konnten erfolgreich synthetisiert und Charakterisiert werden. Deren experimenteller Einsatz zur Synthese der IRMOF-Homologen schlug jedoch fehl. Es konnte gezeigt werden, dass unter den klassischen CSA-Reaktionsbedingungen sowie unter modifizierten Parametern keine Synthese der IRMOF-Homologen möglich ist. Diese Feststellung wurde mit der Diskussion um die Eigenschaften der Komplexe, der Metallionen sowie mit einer Aufarbeitung der dazu zugänglichen Literatur begründet. Es ist mit der Synthese der neuen MOF-177-Homologen MOF-177(Co) und MOF-177(Be) gelungen, die bereits bei MOF-5-Homologen eingesetzten Precursor und Parameter auf ein System anzuwenden, das nicht zu den Yaghi\\\\\\\\\\\\\\\'schen IRMOFs gehört. Die Festkörper weisen mit ihren Oberflächenwerten SBET(MOF-177(Co)) = 3742 m²/g bzw. SBET(MOF-177(Be)) = 1816.4 m²/g klar mikroporöses Adsorptionsverhalten auf. Eine erste vereinfachte Anpassung der Kristallstrukturen an die experimentellen PXRDs konnte für beide MOFs vorgenommen werden. MOF-177(Co) zeigt wie auch MOF-5(Co) eine leicht vergrößerte Gitterkonstante. MOF-177(Be) konnte aufgrund der Verdrehung der Carboxylatgruppen am Berylliumoxocluster ausschließlich in röntgenamorpher Form hergestellt werden. Die Untersuchung der auftretenden Co-Spezies in reinen und mit Zinkprecursor gemischten Lösungen an Cobaltoxopivalat in den Lösungsmitteln Toluol brachte folgende Erkenntnisse: • Der im Feststoff dimere achtkernige Cobaltprecursor zerfällt während des Lösens in die vierkernige monomere Form und ist strukturanalog dem basischen Zinkcarboxylaten (Typ I). • Der Komplex unterliegt einem solvensabhängigem Komplexstabilitäts-gleichgewicht. Dieses ist aufgrund der koordinierenden Eigenschaften des DEF, in den DEF-Lösungen weiter in Richtung der Zersetzungsprodukte verschoben. In beiden Lösungen ist der Komplex zu über 90% undissoziiert. • Nur in DEF treten bei dem Zumischen verschiedener Zinkprecursor Metallaustauschreaktionen auf. Es ist somit die Existenz von vierkernigen Zn-Co-Mischclustern der allg. Form [CoyZn(4-y)O] bewiesen worden. • Es wurde nachgewiesen, dass beim Vorhandensein von Acetat und Pivalat Anionenaustauschreaktionen stattfinden und Komplexe der Form [CoyZn(4-y)O(Piv)xAc(6-x)] auftreten. Die Bedeutung für das Stattfinden des CSAs unter Berücksichtigung der empirischen Erkenntnisse aus der Literatur wurde erörtert.
10

Radical Polymerization Kinetics in Systems with Transfer Reactions Studied by Pulsed-Laser-Polymerization and Online EPR-Detection / Studien zur Kinetik radikalischer Polymerisationen mit zwei Sorten von Radikalspezies durch Pulslaser Polymerisation mit Online EPR-Spektroskopie

Barth, Johannes 25 October 2011 (has links)
No description available.

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