Direct electron transfer to cytochrome c oxidase investigated by electrochemistry and time-resolved surface-enhanced infrared absorption spectroscopy

Cytochrom c Oxidase (CcO), der Komplex IV der Atmungskette, ist eine der Häm-Kupfer enthaltenden Oxidasen und hat eine wichtige Funktion im Zellmetabolismus. Das Enzym enthält vier prosthetische Gruppen und befindet sich in der inneren Membran von Mitochondrien und in der Zellmembran einiger aerober Bakterien. Die CcO katalysiert den Elektronentransfer (ET) von Cytochrom c zu O2, wobei die eigentliche Reaktion am binuklearen Zentrum (CuB-Häm a3) erfolgt. Bei der Reduktion von O2 zu zwei H2O werden vier Protonen verbraucht. Zudem werden vier Protonen über die Membran transportiert, wodurch eine elektrochemische Potentialdifferenz dieser Ionen zwischen Matrix und Intermembranphase entsteht. Trotz ihrer Wichtigkeit sind Membranproteine wie die CcO noch wenig untersucht, weshalb auch der Mechanismus der Atmungskette noch nicht vollständig aufgeklärt ist. Das Ziel dieser Arbeit ist, einen Beitrag zum Verständnis der Funktion der CcO zu leisten. Hierzu wurde die CcO aus Rhodobacter sphaeroides über einen His-Anker, der am C-Terminus der Untereinheit II angebracht wurde, an eine funktionalisierte Metallelektrode in definierter Orientierung gebunden. Der erste Elektronenakzeptor, das CuA, liegt dabei am nächsten zur Metalloberfläche. Dann wurde eine Doppelschicht aus Lipiden insitu zwischen die gebundenen Proteine eingefügt, was zur sog. proteingebundenen Lipid-Doppelschicht Membran (ptBLM) führt. Dabei musste die optimale Oberflächenkonzentration der gebundenen Proteine herausgefunden werden. Elektrochemische Impedanzspektroskopie(EIS), Oberflächenplasmonenresonanzspektroskopie (SPR) und zyklische Voltammetrie (CV) wurden angewandt um die Aktivität der CcO als Funktion der Packungsdichte zu charakterisieren. Der Hauptteil der Arbeit betrifft die Untersuchung des direkten ET zur CcO unter anaeroben Bedingungen. Die Kombination aus zeitaufgelöster oberflächenverstärkter Infrarot-Absorptionsspektroskopie (tr-SEIRAS) und Elektrochemie hat sich dafür als besonders geeignet erwiesen. In einer ersten Studie wurde der ET mit Hilfe von fast scan CV untersucht, wobei CVs von nicht-aktivierter sowie aktivierter CcO mit verschiedenen Vorschubgeschwindigkeiten gemessen wurden. Die aktivierte Form wurde nach dem katalytischen Umsatz des Proteins in Anwesenheit von O2 erhalten. Ein vier-ET-modell wurde entwickelt um die CVs zu analysieren. Die Methode erlaubt zwischen dem Mechanismus des sequentiellen und des unabhängigen ET zu den vier Zentren CuA, Häm a, Häm a3 und CuB zu unterscheiden. Zudem lassen sich die Standardredoxpotentiale und die kinetischen Koeffizienten des ET bestimmen. In einer zweiten Studie wurde tr-SEIRAS im step scan Modus angewandt. Dafür wurden Rechteckpulse an die CcO angelegt und SEIRAS im ART-Modus verwendet um Spektren bei definierten Zeitscheiben aufzunehmen. Aus diesen Spektren wurden einzelne Banden isoliert, die Veränderungen von Vibrationsmoden der Aminosäuren und Peptidgruppen in Abhängigkeit des Redoxzustands der Zentren zeigen. Aufgrund von Zuordnungen aus der Literatur, die durch potentiometrische Titration der CcO ermittelt wurden, konnten die Banden versuchsweise den Redoxzentren zugeordnet werden. Die Bandenflächen gegen die Zeit aufgetragen geben dann die Redox-Kinetik der Zentren wieder und wurden wiederum mit dem vier-ET-Modell ausgewertet. Die Ergebnisse beider Studien erlauben die Schlussfolgerung, dass der ET zur CcO in einer ptBLM mit größter Wahrscheinlichkeit dem sequentiellen Mechanismus folgt, was dem natürlichen ET von Cytochrom c zur CcO entspricht.

Structure and properties of quaternary and tetragonal Heusler compounds for spintronics and spin transfer torque applications

Diese Dissertation ist in zwei Teile aufgeteilt: Teil 1 befasst sich mit der Vorhersage von Halb-Metallizität in quarternären Heuslerverbindungen und deren Potential für Spintronik-Anwendungen. Teil 2 befasst sich mit den strukturellen Eigenschaften der Mn2-basierenden Heuslerverbindungen und dem Tuning von ihrer magnetischen Eigenschaften bzgl. Koerzitivfeldstärke und Remanenz. Diese Verbindungen sind geeignet für Spin-Transfer Torque-Anwendungen.rnrnIn Teil 1 wurden die folgenden drei Probenserien quarternärer Heuslerverbindungen untersucht: XX´MnGa (X = Cu, Ni und X´ = Fe, Co), CoFeMnZ (Z = Al, Ga, Si, Ge) und Co2−xRhxMnZ (Z = Ga, Sn, Sb). Abgesehen von CuCoMnGa wurden alle diese Verbindungen mittels ab-initio Bandstrukturrechnungen als halbmetallische Ferromagnete prognostiziert. In der XX´MnGa-Verbindungsklasse besitzt NiFeMnGa zwar eine zu niedrige Curie-Temperatur für technologische Anwendungen, jedoch NiCoMnGa mit seiner hohen Spinpolarisation, einem hohen magnetischen Moment und einer hohen Curie-Temperatur stellt ein neues Material für Spintronik-Anwendungen dar. Alle CoFeMnZ-Verbindungen kristallisieren in der kubischen Heuslerstruktur und ihre magnetischen Momente folgen der Slater-Pauling-Regel, was Halbmetalizität und eine hohe Spinpolarisation impliziert. Die ebenfalls hohen Curie-Temperaturen ermöglichen einen Einsatz weit über Raumtemperatur hinaus. In der strukturellen Charakterisierung wurde festgestellt, dass sämtliche Co2−xRhxMnZ abgesehen von CoRhMnSn verschiedene Typen von Unordnung aufweisen; daher war die ermittelte Abweichung von der Slater-Pauling-Regel sowie von der 100%-igen Spinpolarisation dieser Verbindungen zu erwarten. Die Halbmetallizität der geordneten CoRhMnSn-Verbindung sollte nach den durchgeführten magnetischen Messungen vorhanden sein.rnrnIm zweiten Teil wurden Mn3−xCoxGa und Mn2−xRh1+xSn synthetisiert und charakterisiert. Es wurde gezeigt, dass Mn3−xCoxGa im Bereich x = 0.1 − 0.4 in einer tetragonal verzerrten inversen Heuslerstruktur kristallisiert und im Bereich x = 0.6−1 in einer kubisch inversen Heuslerstruktur. Während die tetragonalen Materialien hartmagnetisch sind und Charakeristika aufweisen, die typischerweise für Spin-Transfer Torque-Anwengungen attraktiv sind, repräsentieren die weichmagnetischen kubischen Vertreter die 100% spinpolarisierten Materialien, die der Slater-Pauling-Regel folgen. Mn2RhSn kristallisiert in der inversen tetragonal verzerrten Heuslerstruktur, weist einernhartmagnetische Hystereseschleife auf und folgt nicht der Slater-Pauling-Regel. Bei hohen Rh-Gehalt wird die kubische inverse Heuslerstruktur gebildet. Alle kubischen Proben sind weichmagnetisch und folgen der Slater-Pauling-Regel.

Donor–acceptor systems in the quest for organic semiconductors

Die letzten Jahrzehnte brachten eine Vielzahl neuer organischen Halbleiter hervor, welche erfolgreich als aktive Materialien in Bauteilen eingesetzt wurden, wie zum Beispiel Feldeffekttransistoren (FET), organische Leuchtdioden (OLED), organischen Photovoltaikzellen (OPV) und Sensoren. Einige dieser Materialien haben, obwohl sich die Technolgie noch in der „Pubertät“ befindet, die minimalen Anforderungen für eine kommerzielle Anwendung erreicht, wobei jedoch vieles noch zu entdecken, erklären und verstehen bleibt. Diese Arbeit beschreibt das Design, die Synthese und Charakterisierung neuartiger halbleitender Polymere mit speziell eingestellten optoelektronischen Eigenschaften, welche effiziente ambipolare oder n-Leitung in OFET’s und OPV’s zeigen. Das Hauptziel wurde dadurch erreicht, dass sowohl die vorteilhaften Eigenschaften des planaren, elektronenarmen heterozyklischen Bausteines Thiadiazolo[3,4-g]quinoxalin als auch von Ethinbrücken, welche den Donor (D) und den Akzeptor (A) in einem D-A-Copolymer verbinden, durch systematische Optimierung ausgenutzt wurden. Neben synthetischen Herausforderungen werden in dieser Arbeit auch detailiiete Untersuchungen der optoelektronischen Eigenschaften der hergestellten konjugierten Polymere und Modellverbindungen dargelegt. Darüber hinaus beschreibt diese Arbeit erstmals ein Beispiel für ein Polymer, welches Dreifachbindungen im Polymerrückgrat enthält, und nahezu eine ausgeglichene ambipolare Ladungsträgerleitung in OFET’s zeigt. Zusätzlich werden gemischt-valente Phenothiazine, verbrückt mittels elektronenarmen pi-Brücken wie etwa Benzo[c][2,1,3]thiadiazol, und deren Elektronentransferprozesse, im Rahmen der Marcus-Hush-Theorie, untersucht.

Hundertneunundzwanzig Xe NMR for investigations of complex and dynamic systems

In this work, the remarkable versatility and usefulness of applications of Xe-129 NMR experiments is further extended. The application of Xe-129 NMR spectroscopy to very different system is studied, including dynamic and static, solid and liquid, porous and non-porous systems. Using the large non-equilibrium polarization created by hyperpolarization of Xe-129, time-resolved NMR measurements can be used for the online-monitoring of dynamic systems. In the first part of this work, several improvements for medical applications of hyperpolarized Xe-129 are achieved and their feasibility shown experimentally. A large gain in speed and reproducibility of the accumulation process of Xe-129 as ice and an enhancement of the usable polarization in any experiment requiring prior accumulation are achieved. An enhancement of the longitudinal relaxation time of Xe-129 is realized by admixture of a buffer gas during the storage of hyperpolarized Xe-129. Pursuing the efforts of simplifying the accumulation process and enhancing the storage time of hyperpolarized Xe-129 will allow for a wider use of the hyperpolarized gas in (medical) MRI experiments. Concerning the use of hyperpolarized Xe-129 in MRI, the influence of the diffusion coefficient of the gas on parameters of the image contrast is experimentally demonstrated here by admixture of a buffer gas and thus changing the diffusion coefficient. In the second part of this work, a polymer system with unique features is probed by Xe-129 NMR spectroscopy, proving the method to be a valuable tool for the characterization of the anisotropic properties of semicrystalline, syndiotactic polystyrene films. The polymer films contain hollow cavities or channels with sizes in the sub-nanometer range, allowing for adsorption of Xe-129 and subsequent NMR measurements. Despite the use of a ’real-world’ system, the transfer of the anisotropic properties from the material to adsorbed Xe-129 atoms is shown, which was previously only known for fully crystalline materials. The anisotropic behavior towards atomar guests inside the polymer films is proven here for the first time for one of the phases. For the polymer phase containing nanochannels, the dominance of interactions between Xe-129 atoms in the channels compared to interactions between Xe atoms and the channel walls are proven by measurements of a powder sample of the polymer material and experiments including the rotation of the films in the external magnetic field as well as temperature-dependent measurements. The characterization of ’real-world’ systems showing very high degrees of anisotropy by Xe-129 are deemed to be very valuable in future applications. In the last part of this work, a new method for the online monitoring of chemical reactions has been proposed and its feasibility and validity are experimentally proven. The chemical shift dependence of dissolved Xe-129 on the composition of a reaction mixture is used for the online monitoring of free-radical miniemulsion polymerization reactions. Xe-129 NMR spectroscopy provides an excellent method for the online monitoring of polymerization reactions, due to the simplicity of the Xe-129 NMR spectra and the simple relationship between the Xe-129 chemical shift and the reaction conversion. The results of the time-resolved Xe-129 NMR measurements are compared to those from calorimetric measurements, showing a good qualitative agreement. The applicability of the new method to reactions other than polymerization reactions is investigated by the online monitoring of an enzymatic reaction in a miniemulsion. The successful combination of the large sensitivity of Xe-129, the NMR signal enhancements due to hyperpolarization, and the solubility of Xe-129 gives access to the large new field of investigations of chemical reaction kinetics in dynamic and complex systems like miniemulsions.

Structure formation of amphiphilic molecules at the air,water interface and after film transfer

One of the basic concepts of molecular self-assembly is that the morphology of the aggregate is directly related to the structure and interaction of the aggregating molecules. This is not only true for the aggregation in bulk solution, but also for the formation of Langmuir films at the air/water interface. Thus, molecules at the interface do not necessarily form flat monomolecular films but can also aggregate into multilayers or surface micelles. In this context, various novel synthetic molecules were investigated in terms of their morphology at the air/water interface and in transferred films. rnFirst, the self-assembly of semifluorinated alkanes and their molecular orientation at the air/water interface and in transferred films was studied employing scanning force microscopy (SFM) and Kelvin potential force microscopy. Here it was found, that the investigated semifluorinated alkanes aggregate to form circular surface micelles with a diameter of 30 nm, which are constituted of smaller muffin-shaped subunits with a diameter of 10 nm. A further result is that the introduction of an aromatic core into the molecular structure leads to the formation of elongated surface micelles and thus implements a directionality to the self-assembly. rnSecond, the self-assembly of two different amphiphilic hybrid materials containing a short single stranded desoxyribonucleic acid (DNA) sequence was investigated at the air/water interface. The first molecule was a single stranded DNA (11mer) molecule with two hydrophobically modified 5-(dodec-1-ynyl)uracil nucleobases at the terminal 5'-end of the oligonucleotide sequence. Isotherm measurements revealed the formation of semi-stable films at the air/water interface. SFM imaging of films transferred via Langmuir-Blodgett technique supported this finding and indicated mono-, bi- and multilayer formation, according to the surface pressure applied upon transfer. Within these films, the hydrophilic DNA sequence was oriented towards air covering 95% of the substrate.rnSimilar results were obtained with a second type of amphiphile, a DNA block copolymer. Furthermore, the potential to perform molecular recognition experiments at the air/water interface with these DNA hybrid materials was evaluated.rnThird, polyglycerol ester molecules (PGE), which are known to form very stable foams, were studies. Aim was to elucidate the molecular structure of PGE molecules at the air/water interface in order to comprehend the foam stabilization mechanism. Several model systems mimicking the air/water interface of a PGE foam and methods for a noninvasive transfer were tested and characterized by SFM. It could be shown, that PGE stabilizes the air/water interface of a foam bubble by formation of multiple surfactant layers. Additionally, a new transfer technique, the bubble film transfer was established and characterized by high speed camera imaging.The results demonstrate the diversity of structures, which can be formed by amphiphilic molecules at the air/water interface and after film transfer, as well as the impact of the chemical structure on the aggregate morphology.

Structure, Dynamics and Reactivity in the Organic Solid State: Anthracene Derivatives and Charge Transfer Crystals

The work presented in this thesis tackles some important points concerning the collective properties of two typical categories of molecular crystals, i.e., anthracene derivatives and charge transfer crystals. Anthracene derivatives have constituted the class of materials from which systematical investigations of crystal-to-crystal photodimerization reactions started, developed and have been the subject of a new awakening in the recent years. In this work some of these compounds, namely, 9-cyanoanthacene, 9-anthacenecarboxylic acid and 9-methylanthracene, have been selected as model systems for a phenomenological approach to some key properties of the solid state, investigated by spectroscopic methods. The present results show that, on the basis of the solid state organization and the chemical nature of each compound, photo-reaction dynamics and kinetics display distinctive behaviors, which allows for a classification of the various processes in topochemical, non topochemical, reversible or topophysical. The second part of the thesis was focused on charge transfer crystals, binary systems formed by stoichiometric combinations of the charge donating perylene (D) and the charge accepting tetracyano-quinodimethane (A), this latter also in its fluorinated derivatives. The work was focused on the growth of single crystals, some of which not yet reported in the literature, by PVT technique. Structural and spectroscopic characterizations have been performed, with the aim of determining the degree of charge transfer between donor and acceptor in the co-crystals. An interesting outcome of the systematic search performed in this work is the definition of the experimental conditions which drive the crystal growth of the binary systems either towards the low (1:1) or the high ratio (3:1 or 3:2) stoichiometries.

Photophysical investigation of light-harvesting systems for solar-to-fuel conversion

In recent years, an increasing attention has been given to the optimization of the performances of new supramolecular systems, as antennas for light collection. In such background, the aim of this thesis was the study of multichromophoric architectures capable of performing such basic action. A synthetic antenna should consist of a structure with large UV-Vis absorption cross-section, panchromatic absorption, fixed orientation of the components and suitable energy gradients between them, in order to funnel absorbed energy towards a specific site, through fast energy-transfer processes. Among the systems investigated in this thesis, three suitable classes of compounds can be identified: 1) transition metal-based multichromophoric arrays, as models for antenna construction, 2) free-base trans-A2B-phenylcorroles, as self-assembling systems to make effective mimics of the photosynthetic system, and 3) a natural harvester, the Photosystem I, immobilized on the photoanode of a solar-to-fuel conversion device. The discussion starts with the description of the photophysical properties of dinuclear quinonoid organometallic systems, able to fulfil some of the above mentioned absorption requirements, displaying in some cases panchromatic absorption. The investigation is extended to the efficient energy transfer processes occurring in supramolecular architectures, suitably organized around rigid organic scaffolds, such as spiro-bifluorene and triptycene. Furthermore, the photophysical characterization of three trans-A2B-phenylcorroles with different substituents on the meso-phenyl ring is introduced, revealing the tendency of such macrocycles to self-organize into dimers, by mimicking natural self-aggregates antenna systems. In the end, the photophysical analysis moved towards the natural super-complex PSI-LHCI, immobilized on the hematite surface of the photoanode of a bio-hybrid dye-sensitized solar cell. The importance of the entire work is related to the need for a deep understanding of the energy transfer mechanisms occurring in supramolecules, to gain insights and improve the strategies for governing the directionality of the energy flow in the construction of well-performing antenna systems.

In vitro characterization of human AML-reactive CTL clones generated from the naive subset of healthy donors and adoptive transfer into leukemia-engrafted NSG mice

Acute myeloid leukemia (AML) is a very aggressive cancer of the hematopoietic system. Chemotherapy and immunotherapeutical approaches including hematopoietic stem cell transplantation (HSCT) and donor lymphocyte infusion (DLI) are the only curative options available. The beneficial graft-versus-leukemia (GVL) effect of cellular immunotherapy is mostly mediated by donor-derived CD8+ T lymphocytes that recognize minor histocompatibility antigens (mHags) and leukemia-associated antigens (LAAs) presented on the surface of AML blasts (Falkenburg et al. 2008; Kolb 2008). A main complication is graft-versus-host disease (GVHD) that can be induced when cytotoxic T lymphocytes (CTLs) recognize broadly expressed antigens. To reduce the risk of GVHD, specific allogeneic T-cell therapy inducing selective GVL responses could be an option (Barrett & Le Blanc 2010; Parmar et al. 2011; Smits et al. 2011). This requires efficient in vitro strategies to generate AML-reactive T cells with an early differentiation phenotype as well as vigorous effector functions and humanized mouse models to analyze the anti-leukemic potential of adoptively transferred T cells in vivo. In this study, AML-reactive CTL clones and oligoclonal T-cell lines could be reliably generated from the naive subset of healthy HLA-class I-identical donors by stimulation with primary AML blasts in mini-mixed-lymphocyte / leukemia cultures (MLLCs) in eight different patient / donor pairs. These CTLs were promising candidates for cellular immunotherapy because of their relatively early differentiation phenotype and strong proliferative and lytic capabilities. The addition of the common γ-chain cytokine IL-21 to the stimulation protocol enabled more precursors to develop into potent leukemia-reactive CTLs, presumably by its beneficial effects on cell survival and antigen-specific proliferation during the first weeks of cultures. It also strengthened the early-stage phenotype. Three long-term cultured CTLs exemplarily transferred into leukemia-engrafted immunodeficient NSG mice mediated a significant reduction of the leukemic burden after a single transfusion. These results demonstrate that CTL clones with reactivity to patient-derived AML blasts can be isolated from the naive compartment of healthy donors and show potent anti-leukemic effects in vivo. The herein described allo-MLLC approach with in vitro “programmed” naive CTL precursors independent of a HSCT setting is a valuable alternative to the conventional method of isolating in vivo primed donor CTLs out of patients after transplantation (Kloosterboer et al. 2004; Warren et al. 2010). This would make leukemia-reactive CTLs already available at the time point of HSCT, when residual leukemia disease is minimal and the chances for complete leukemia eradication are high. Furthermore, leukemia-reactive CTLs effectively expanded by this in vitro protocol can be used as screening populations to identify novel candidate LAAs and mHags for antigen-specific immunotherapy.

Noncoherent upconversion in multimolecular organic systems

The dissertation is devoted to the investigation of the process of triplet-triplet annihilation assisted upconversion (TTA – UC). The current state of the art of the used nowadays emitters and sensitizers was overviewed. The new emitters, synthesized mainly on the base of perylene, were created and analyzed for the applicability for TTA – UC in the combination with the sensitizers from tetrabenzo- and tetranaphtoporphyrin families. A strong influence of the excitation beam parameters on UC efficiency was shown. The new strategy of an effective UC emitter’s creation by comprising the functions of two chromophors in a dyad, where the function of the triplet-triplet transfer (TTT) and the triplet-triplet annihilation (TTA) are attributed to different parts of the molecule, was represented. The successful transfer of an UC medium into the water environment by the encapsulation of hydrophobic UC dyes into the micelles, formed by the PTS surfactant, was done. Resulting quantum efficiency is comparable with that in an organic solvent. An extremely strong dependence of the efficiency of the TTA – UC process on temperature in such micellar structures was obtained

Excited-state dynamics in donor-acceptor systems for energy conversion

In dieser Arbeit werden die Dynamiken angeregter Zustände in Donor-Akzeptorsystemen für Energieumwandlungsprozesse mit ultraschneller zeitaufgelöster optischer Spektroskopie behandelt. Der Hauptteil dieser Arbeit legt den Fokus auf die Erforschung der Photophysik organischer Solarzellen, deren aktive Schichten aus diketopyrrolopyrrole (DPP) basierten Polymeren mit kleiner Bandlücke als Elektronendonatoren und Fullerenen als Elektronenakzeptoren bestehen. rnEin zweiter Teil widmet sich der Erforschung von künstlichen primären Photosynthesereaktionszentren, basierend auf Porphyrinen, Quinonen und Ferrocenen, die jeweils als Lichtsammeleinheit, Elektronenakzeptor beziehungsweise als Elektronendonatoren eingesetzt werden, um langlebige ladungsgetrennte Zustände zu erzeugen.rnrnZeitaufgelöste Photolumineszenzspektroskopie und transiente Absorptionsspektroskopie haben gezeigt, dass Singulettexzitonenlebenszeiten in den Polymeren PTDPP-TT und PFDPP-TT Polymeren kurz sind (< 20 ps) und dass in Mischungen der Polymere mit PC71BM geminale Rekombination von gebundenen Ladungstransferzuständen ein Hauptverlustkanal ist. Zudem wurde in beiden Systemen schnelle nichtgeminale Rekombination freier Ladungen zu Triplettzuständen auf dem Polymer beobachtet. Für das Donor-Akzeptor System PDPP5T:PC71BM wurde nachgewiesen, dass die Zugabe eines Lösungsmittels mit hohem Siedepunkt, und zwar ortho-Dichlorbenzol, die Morphologie der aktiven Schicht stark beeinflusst und die Solarzelleneffizienz verbessert. Der Grund hierfür ist, dass die Donator- und Akzeptormaterialien besser durchmischt sind und sich Perkolationswege zu den Elektroden ausgebildet haben, was zu einer verbesserten Ladungsträgergeneration und Extraktion führt. Schnelle Bildung des Triplettzustands wurde in beiden PDPP5T:PC71BM Systemen beobachtet, da der Triplettzustand des Polymers über Laungstransferzustände mit Triplettcharakter populiert werden kann. "Multivariate curve resolution" (MCR) Analyse hat eine starke Intensitätsabhängigkeit gezeigt, was auf nichtgeminale Ladungsträgerrekombination in den Triplettzustand hinweist.rnrnIn den künstlichen primären Photosynthesereaktionszentren hat transiente Absorptionsspektroskopie bestätigt, dass photoinduzierter Ladungstransfer in Quinon-Porphyrin (Q-P) und Porphyrin-Ferrocen (P-Fc) Diaden sowie in Quinon-Porphyrin-Ferrocen (Q-P-Fc) Triaden effizient ist. Es wurde jedoch auch gezeigt, dass in den P-Fc unf Q-P-Fc Systemen die ladungsgetrennten Zustände in den Triplettzustand der jeweiligen Porphyrine rekombinieren. Der ladungsgetrennte Zustand konnte in der Q-P Diade durch Zugabe einer Lewissäure signifikant stabilisiert werden.

Synthesis, characterization and catalytic performances of ruthenium-based catalysts for the acceptorless dehydrogenative coupling of butanol

A growing interest towards new sources of energy has led in recent years to the development of a new generation of catalysts for alcohol dehydrogenative coupling (ADC). This green, atom-efficient reaction is capable of turning alcohol derivatives into higher value and chemically more attractive ester molecules, and it finds interesting applications in the transformation of the large variety of products deriving from biomass. In the present work, a new series of ruthenium-PNP pincer complexes are investigated for the transformation of 1-butanol, one of the most challenging substrates for this type of reactions, into butyl butyrate, a short-chain symmetrical ester widely used in flavor industries. Since the reaction kinetics depends on hydrogen diffusion, the study aimed at identifying proper reactor type and right catalyst concentration to avoid mass transfer interferences and to get dependable data. A comparison between catalytic activities and productivities has been made to establish the role of the different ligands bonded both to the PNP binder and to the ruthenium metal center, and hence to find the best catalyst for this type of reaction.

Evaluating Code Duplication to Identify Rich Business Objects from Data Transfer Objects

Java Enterprise Applications (JEAs) are complex software systems written using multiple technologies. Moreover they are usually distributed systems and use a database to deal with persistence. A particular problem that appears in the design of these systems is the lack of a rich business model. In this paper we propose a technique to support the recovery of such rich business objects starting from anemic Data Transfer Objects (DTOs). Exposing the code duplications in the application's elements using the DTOs we suggest which business logic can be moved into the DTOs from the other classes.

Single- and double-electron transfer reactions of ground and metastable state Ar2+ ions

Electron transfer cross sections have been measured for reactions of Ar2+ ions with Ar, N2, O2, CO2, CH4 and C2H6. Time-of-flight techniques have been used to measure both fast neutral Ar0 and fast Ar+ products from single- and double-electron transfer processes involving Ar2+ ions with 4.0 to 7.0 keV impact energies. Incident Ar2+ ions have produced by controlled electron impact ionisation of argon atoms. Reactions have been examined as a function of ionising electron energy and cross sections determined for ground state Ar2+(3P) ions. Charge transfer cross sections have been determined to be in the range of 3*10-16 cm2 for the systems examined. Double-electron transfer cross sections are the same order of magnitude as those measured for the corresponding single-electron transfer reactions. The state distribution of the reactant ion beam has been estimated and electron transfer cross sections obtained for single- and double-electron transfer reactions of metastable Ar2+ions. The magnitudes of electron transfer cross sections in individual systems are similar for both ground and metastable state Ar2+ reactions.

Charge transfer reactions of organic ions containing oxygen: Correlation between reaction energetics and cross sections

Cross sections for charge transfer reactions of organic ions containing oxygen have been obtained using time-of-flight techniques. Charge transfer cross sections have been determined for reactions of 2.0 to 3.4 keV ions produced by electron impact ionization of oxygen containing molecules such as methanol, ethanal and ethanol. Experimental cross section magnitudes have been correlated with reaction energy defects computed from ion recombination energies and target ionization energies. Large cross sections are observed for reacting systems with small energy defects.

Uncovering the dynamics of cardiac systems using stochastic pacing and frequency domain analyses

Alternans of cardiac action potential duration (APD) is a well-known arrhythmogenic mechanism which results from dynamical instabilities. The propensity to alternans is classically investigated by examining APD restitution and by deriving APD restitution slopes as predictive markers. However, experiments have shown that such markers are not always accurate for the prediction of alternans. Using a mathematical ventricular cell model known to exhibit unstable dynamics of both membrane potential and Ca2+ cycling, we demonstrate that an accurate marker can be obtained by pacing at cycle lengths (CLs) varying randomly around a basic CL (BCL) and by evaluating the transfer function between the time series of CLs and APDs using an autoregressive-moving-average (ARMA) model. The first pole of this transfer function corresponds to the eigenvalue (λalt) of the dominant eigenmode of the cardiac system, which predicts that alternans occurs when λalt≤−1. For different BCLs, control values of λalt were obtained using eigenmode analysis and compared to the first pole of the transfer function estimated using ARMA model fitting in simulations of random pacing protocols. In all versions of the cell model, this pole provided an accurate estimation of λalt. Furthermore, during slow ramp decreases of BCL or simulated drug application, this approach predicted the onset of alternans by extrapolating the time course of the estimated λalt. In conclusion, stochastic pacing and ARMA model identification represents a novel approach to predict alternans without making any assumptions about its ionic mechanisms. It should therefore be applicable experimentally for any type of myocardial cell.