Studies of OPA1 pathogenic mechanisms in Dominant Optic Atrophy and novel protein function in mitochondrial DNA stability

The mitochondrion is an essential cytoplasmic organelle that provides most of the energy necessary for eukaryotic cell physiology. Mitochondrial structure and functions are maintained by proteins of both mitochondrial and nuclear origin. These organelles are organized in an extended network that dynamically fuses and divides. Mitochondrial morphology results from the equilibrium between fusion and fission processes, controlled by a family of “mitochondria-shaping” proteins. It is becoming clear that defects in mitochondrial dynamics can impair mitochondrial respiration, morphology and motility, leading to apoptotic cell death in vitro and more or less severe neurodegenerative disorders in vivo in humans. Mutations in OPA1, a nuclear encoded mitochondrial protein, cause autosomal Dominant Optic Atrophy (DOA), a heterogeneous blinding disease characterized by retinal ganglion cell degeneration leading to optic neuropathy (Delettre et al., 2000; Alexander et al., 2000). OPA1 is a mitochondrial dynamin-related guanosine triphosphatase (GTPase) protein involved in mitochondrial network dynamics, cytochrome c storage and apoptosis. This protein is anchored or associated on the inner mitochondrial membrane facing the intermembrane space. Eight OPA1 isoforms resulting from alternative splicing combinations of exon 4, 4b and 5b have been described (Delettre et al., 2001). These variants greatly vary among diverse organs and the presence of specific isoforms has been associated with various mitochondrial functions. The different spliced exons encode domains included in the amino-terminal region and contribute to determine OPA1 functions (Olichon et al., 2006). It has been shown that exon 4, that is conserved throughout evolution, confers functions to OPA1 involved in maintenance of the mitochondrial membrane potential and in the fusion of the network. Conversely, exon 4b and exon 5b, which are vertebrate specific, are involved in regulation of cytochrome c release from mitochondria, and activation of apoptosis, a process restricted to vertebrates (Olichon et al., 2007). While Mgm1p has been identified thanks to its role in mtDNA maintenance, it is only recently that OPA1 has been linked to mtDNA stability. Missense mutations in OPA1 cause accumulation of multiple deletions in skeletal muscle. The syndrome associated to these mutations (DOA-1 plus) is complex, consisting of a combination of dominant optic atrophy, progressive external ophtalmoplegia, peripheral neuropathy, ataxia and deafness (Amati- Bonneau et al., 2008; Hudson et al., 2008). OPA1 is the fifth gene associated with mtDNA “breakage syndrome” together with ANT1, PolG1-2 and TYMP (Spinazzola et al., 2009). In this thesis we show for the first time that specific OPA1 isoforms associated to exon 4b are important for mtDNA stability, by anchoring the nucleoids to the inner mitochondrial membrane. Our results clearly demonstrate that OPA1 isoforms including exon 4b are intimately associated to the maintenance of the mitochondrial genome, as their silencing leads to mtDNA depletion. The mechanism leading to mtDNA loss is associated with replication inhibition in cells where exon 4b containing isoforms were down-regulated. Furthermore silencing of exon 4b associated isoforms is responsible for alteration in mtDNA-nucleoids distribution in the mitochondrial network. In this study it was evidenced that OPA1 exon 4b isoform is cleaved to provide a 10kd peptide embedded in the inner membrane by a second transmembrane domain, that seems to be crucial for mitochondrial genome maintenance and does correspond to the second transmembrane domain of the yeasts orthologue encoded by MGM1 or Msp1, which is also mandatory for this process (Diot et al., 2009; Herlan et al., 2003). Furthermore in this thesis we show that the NT-OPA1-exon 4b peptide co-immuno-precipitates with mtDNA and specifically interacts with two major components of the mitochondrial nucleoids: the polymerase gamma and Tfam. Thus, from these experiments the conclusion is that NT-OPA1- exon 4b peptide contributes to the nucleoid anchoring in the inner mitochondrial membrane, a process that is required for the initiation of mtDNA replication and for the distribution of nucleoids along the network. These data provide new crucial insights in understanding the mechanism involved in maintenance of mtDNA integrity, because they clearly demonstrate that, besides genes implicated in mtDNA replications (i.e. polymerase gamma, Tfam, twinkle and genes involved in the nucleotide pool metabolism), OPA1 and mitochondrial membrane dynamics play also an important role. Noticeably, the effect on mtDNA is different depending on the specific OPA1 isoforms down-regulated, suggesting the involvement of two different combined mechanisms. Over two hundred OPA1 mutations, spread throughout the coding region of the gene, have been described to date, including substitutions, deletions or insertions. Some mutations are predicted to generate a truncated protein inducing haploinsufficiency, whereas the missense nucleotide substitutions result in aminoacidic changes which affect conserved positions of the OPA1 protein. So far, the functional consequences of OPA1 mutations in cells from DOA patients are poorly understood. Phosphorus MR spectroscopy in patients with the c.2708delTTAG deletion revealed a defect in oxidative phosphorylation in muscles (Lodi et al., 2004). An energetic impairment has been also show in fibroblasts with the severe OPA1 R445H mutation (Amati-Bonneau et al., 2005). It has been previously reported by our group that OPA1 mutations leading to haploinsufficiency are associated in fibroblasts to an oxidative phosphorylation dysfunction, mainly involving the respiratory complex I (Zanna et al., 2008). In this study we have evaluated the energetic efficiency of a panel of skin fibroblasts derived from DOA patients, five fibroblast cell lines with OPA1 mutations causing haploinsufficiency (DOA-H) and two cell lines bearing mis-sense aminoacidic substitutions (DOA-AA), and compared with control fibroblasts. Although both types of DOA fibroblasts maintained a similar ATP content when incubated in a glucose-free medium, i.e. when forced to utilize the oxidative phosphorylation only to produce ATP, the mitochondrial ATP synthesis through complex I, measured in digitonin-permeabilized cells, was significantly reduced in cells with OPA1 haploinsufficiency only, whereas it was similar to controls in cells with the missense substitutions. Furthermore, evaluation of the mitochondrial membrane potential (DYm) in the two fibroblast lines DOA-AA and in two DOA-H fibroblasts, namely those bearing the c.2819-2A>C mutation and the c.2708delTTAG microdeletion, revealed an anomalous depolarizing response to oligomycin in DOA-H cell lines only. This finding clearly supports the hypothesis that these mutations cause a significant alteration in the respiratory chain function, which can be unmasked only when the operation of the ATP synthase is prevented. Noticeably, oligomycin-induced depolarization in these cells was almost completely prevented by preincubation with cyclosporin A, a well known inhibitor of the permeability transition pore (PTP). This results is very important because it suggests for the first time that the voltage threshold for PTP opening is altered in DOA-H fibroblasts. Although this issue has not yet been addressed in the present study, several are the mechanisms that have been proposed to lead to PTP deregulation, including in particular increased reactive oxygen species production and alteration of Ca2+ homeostasis, whose role in DOA fibroblasts PTP opening is currently under investigation. Identification of the mechanisms leading to altered threshold for PTP regulation will help our understanding of the pathophysiology of DOA, but also provide a strategy for therapeutic intervention.

In situ real-time investigation of Organic Ultra-Thin-Film transistors: growth, electrical properties and biosensing applications

Organic electronics has grown enormously during the last decades driven by the encouraging results and the potentiality of these materials for allowing innovative applications, such as flexible-large-area displays, low-cost printable circuits, plastic solar cells and lab-on-a-chip devices. Moreover, their possible field of applications reaches from medicine, biotechnology, process control and environmental monitoring to defense and security requirements. However, a large number of questions regarding the mechanism of device operation remain unanswered. Along the most significant is the charge carrier transport in organic semiconductors, which is not yet well understood. Other example is the correlation between the morphology and the electrical response. Even if it is recognized that growth mode plays a crucial role into the performance of devices, it has not been exhaustively investigated. The main goal of this thesis was the finding of a correlation between growth modes, electrical properties and morphology in organic thin-film transistors (OTFTs). In order to study the thickness dependence of electrical performance in organic ultra-thin-film transistors, we have designed and developed a home-built experimental setup for performing real-time electrical monitoring and post-growth in situ electrical characterization techniques. We have grown pentacene TFTs under high vacuum conditions, varying systematically the deposition rate at a fixed room temperature. The drain source current IDS and the gate source current IGS were monitored in real-time; while a complete post-growth in situ electrical characterization was carried out. At the end, an ex situ morphological investigation was performed by using the atomic force microscope (AFM). In this work, we present the correlation for pentacene TFTs between growth conditions, Debye length and morphology (through the correlation length parameter). We have demonstrated that there is a layered charge carriers distribution, which is strongly dependent of the growth mode (i.e. rate deposition for a fixed temperature), leading to a variation of the conduction channel from 2 to 7 monolayers (MLs). We conciliate earlier reported results that were apparently contradictory. Our results made evident the necessity of reconsidering the concept of Debye length in a layered low-dimensional device. Additionally, we introduce by the first time a breakthrough technique. This technique makes evident the percolation of the first MLs on pentacene TFTs by monitoring the IGS in real-time, correlating morphological phenomena with the device electrical response. The present thesis is organized in the following five chapters. Chapter 1 makes an introduction to the organic electronics, illustrating the operation principle of TFTs. Chapter 2 presents the organic growth from theoretical and experimental points of view. The second part of this chapter presents the electrical characterization of OTFTs and the typical performance of pentacene devices is shown. In addition, we introduce a correcting technique for the reconstruction of measurements hampered by leakage current. In chapter 3, we describe in details the design and operation of our innovative home-built experimental setup for performing real-time and in situ electrical measurements. Some preliminary results and the breakthrough technique for correlating morphological and electrical changes are presented. Chapter 4 meets the most important results obtained in real-time and in situ conditions, which correlate growth conditions, electrical properties and morphology of pentacene TFTs. In chapter 5 we describe applicative experiments where the electrical performance of pentacene TFTs has been investigated in ambient conditions, in contact to water or aqueous solutions and, finally, in the detection of DNA concentration as label-free sensor, within the biosensing framework.

Dietary strategies to minimize the detrimental impact of weaning on gut morphology, physiology and microbiota of piglets

Weaning is a crucial period in the management of piglets. In modern piggeries economic interest make weaning age decrease more and more and the detrimental consequences of weaning have as much importance as earlier the weaning occurs. The risk of development of post-weaning diarrhea (PWD) in piglets is high and PWD is the cause of serious economic losses in pig herds. In the past the supplementation of the feed given after weaning with growth promoters antibiotics, in order to keep PWD under control, used to be a common practice, but their usage has been banned in EU since 2006. This measure led to the investigation of alternative suitable feed supplements that would be reasonably efficient in protecting and sustaining animal health and performance. Aim of this thesis was to evaluate the effect of some different alternatives to growth-promoters antibiotics on weaning piglets and to assess if some of them could be considered as valuables options to replace auxinic in animal feeding. The study is composed by four experimental trials. The first one aims to identify mechanisms involved in the auxinic effects of antibiotics in the diets; the following three evaluate the addition butyric acid, tryptophan, and nitrate as alternative to in-feed antimicrobials. Although some results are controversial, it appears from the data presented that the alternatives to in-feed antibiotics considered may exert positive effects on some zootechnical and health parameters on piglet in the post-weaning period. Anyway, the mechanism of action and the interaction with microbiota of such additives should be investigated inside out because many effects remains poorly understood.

The physical city and the urban structure: detecting amenity zones and applying urban morphology to New York

The city is a collection of built structures and infrastructure embedded in socio-cultural processes: any investigation into a city’s transformations involves considerations on the degree to which its composite elements respond to socio-economical changes. The main purpose of this research is to investigate how transformations in the functional requirements of New York’s society have spurred, since the 1970s, changes in both the city’s urban structure and physical form. The present work examines the rise of Amenity Zones in New York, and investigates the transformations that have occurred in New York’s built environment since the 1970s. By applying qualitative measures and analyzing the relationship between urban amenities and the creative class, the present work has investigated changes in the urban structure and detected a hierarchical series of amenity zones classes, namely, Super Amenity Zones (SAZs), Nodal Amenity Zones (NAZs) and Peripheral Amenity Zones (PAZs). This series allows for a more comprehensive reading of the urban structure in a complex city like New York, bringing advancements to the amenity zone’s methodology. In order to examine the manner in which the other component of the city, the physical form, has changed or adapted to the new socio-economic condition, the present research has applied Conzenian analysis to a select study area, Atlantic Avenue. The results of this analysis reveal that, contrary to the urban structure, which changes rapidly, the physical form of New York is hard to modify completely, due to the resilience of the town plan and its elements, and to preservation laws; the city rather adapts to socio-economical changes through process of adaptive reuses or conversion. Concluding, this research has examined the dialectic between the ever-changing needs of society and the complexity of the built environment and urban structure, showing the different degrees to which the urban landscape modifies, reacts and sometimes adapts to the population’s functional requirements.

Supramolecular approaches to organized luminescent nanostructures for sensing, labeling and imaging applications

The common thread of this thesis is the will of investigating properties and behavior of assemblies. Groups of objects display peculiar properties, which can be very far from the simple sum of respective components’ properties. This is truer, the smaller is inter-objects distance, i.e. the higher is their density, and the smaller is the container size. “Confinement” is in fact a key concept in many topics explored and here reported. It can be conceived as a spatial limitation, that yet gives origin to unexpected processes and phenomena based on inter-objects communication. Such phenomena eventually result in “non-linear properties”, responsible for the low predictability of large assemblies. Chapter 1 provides two insights on surface chemistry, namely (i) on a supramolecular assembly based on orthogonal forces, and (ii) on selective and sensitive fluorescent sensing in thin polymeric film. In chapters 2 to 4 confinement of molecules plays a major role. Most of the work focuses on FRET within core-shell nanoparticles, investigated both through a simulation model and through experiments. Exciting results of great applicative interest are drawn, such as a method of tuning emission wavelength at constant excitation, and a way of overcoming self-quenching processes by setting up a competitive deactivation channel. We envisage applications of these materials as labels for multiplexing analysis, and in all fields of fluorescence imaging, where brightness coupled with biocompatibility and water solubility is required. Adducts of nanoparticles and molecular photoswitches are investigated in the context of superresolution techniques for fluorescence microscopy. In chapter 5 a method is proposed to prepare a library of functionalized Pluronic F127, which gives access to a twofold “smart” nanomaterial, namely both (i)luminescent and (ii)surface-functionalized SCSSNPs. Focus shifts in chapter 6 to confinement effects in an upper size scale. Moving from nanometers to micrometers, we investigate the interplay between microparticles flowing in microchannels where a constriction affects at very long ranges structure and dynamics of the colloidal paste.

Studio analitico della cultura materiale fra VII e IX secolo d.C. nella Regione di Samarcanda (Uzbekistan): analisi morfo-tipologica, produzione e commercio della ceramica di Kafir Kala

Kafir Kala is a key-site to understand the historical dynamics of the Samarkand Region in the Early Middle Ages (5th - 8th centuries CE). The site is clearly associated with a Sogdian occupation, as both literature and archaeological research testify. But the chronological phase that follows the Sogdian period, as the Islamic occupation became stable, is still little known. Structures and finds (an hoard of 133 silver coins, in particular) clearly testify a new occupation of some parts of the citadel; and some rooms, dug in the northern side of it, present structures and materials connected with an Islamic activity. The study of material culture from these rooms, and from more ancient contexts, will help to understand the eventual continuity of traditions and the new productions. Besides the citadel, as a matter of fact, also some kilns have been dug, near the main site. Their material culture is very interesting because it represents an example of the typical Sogdian production (ceramics covered with white mica, and stamped). The work on the ceramic material has consisted in cataloguing and classifying all the diagnostics. Three main morphological classes have been individuated: cooking, coarse and table ware), and some other ones (lamps, ossuaries). A catalogue of the finds organized them in a typological system based on their morphology, function, fabric, and eventually decoration style. Crossing the stratigraphical data with information from this typological study, it has been possible to provide a chronological arrangement of the sites investigated by the italo-uzbek archaeological mission from 2001 to 2008.

Photovoltaics from discotic liquid crystalline HBCs & poly(2,7-carbazole)s

In this study, the use of the discotic liquid crystalline HBCs and conjugated polymers based on 2,7-carbazole were investigated in detail as donor materials in organic bulk-heterojunction solar cells. It has been shown that they perform efficiently in photovoltaic devices in combination with suitable acceptors. The efficiency was found to depend strongly dependent on the morphology of the film. By investigation of a series of donor materials with similar molecular structures based on both discotic molecules and conjugated polymers, a structure-performance relation was established, which is not only instructive for these materials but also serves as a guideline for improved molecular design. For the series of HBCs used in this study, it is found that the device efficiency decreases with increasing length of the alkyl substituents in the HBC. Thus, the derivative with the smallest alkyl mantle, being more crystalline compared to the HBCs with longer alkyl chains, gave the highest EQE of 12%. A large interfacial separation was found in the blend of HBC-C6,2 and PDI, since the crystallization of the acceptor occurred in a solid matrix of HBC. This led to small dispersed organized domains and benefited the charge transport. In contrast, blends of HBC-C10,6/PDI or HBC-C14,10/PDI revealed a rather homogeneous film limiting the percolation pathways due to a mixed phase. For the first time, poly(2,7-carbazole) was incorporated as a donor material in solar cells using PDI as an electron acceptor. The good fit in orbital energy levels and absorption spectra led to high efficiency. This result indicates that conjugated polymers with high band-gap can also be applied as materials to build efficient solar cells if appropriate electron acceptors are chosen. In order to enhance the light absorption ability, new ladder-type polymers based on pentaphenylene and hexaphenylene with one and three nitrogen bridges per repeat unit have been synthesized and characterized. The polymer 2 with three nitrogen bridges showed more red-shifted absorbance and emission and better packing in the solid-state than the analogous polymer 3 with only one nitrogen bridge per monomer unit. An overall efficiency as high as 1.3% under solar light was obtained for the device based on 1 and PDI, compared with 0.7% for the PCz based device. Therefore, the device performance correlates to a large extent with the solar light absorption ability and the lateral distance between conjugated polymer chains. Since the lateral distance is determined by the length and number of attached alkyl side chains, it is possible to assume that these substituents insulate the charge carrier pathways and decrease the device performance. As an additional consequence, the active semiconductor is diluted in the insulating matrix leading to a lower light absorption. This work suggests ways to improve device performance by molecular design, viz. maintaining the HOMO level while bathochromically shifting the absorption by adopting a more rigid ladder-type structure. Also, a high ratio of nitrogen bridges with small alkyl substituents was a desirable feature both in terms of adjusting the absorption and maintaining a low lateral inter-chain separation, which was necessary for obtaining high current and efficiency values.

Nanotechnology control of self organized biomolecules and biomaterials for medical research

Nanotechnology entails the manufacturing and manipulation of matter at length scales ranging from single atoms to micron-sized objects. The ability to address properties on the biologically-relevant nanometer scale has made nanotechnology attractive for Nanomedicine. This is perceived as a great opportunity in healthcare especially in diagnostics, therapeutics and more in general to develop personalized medicine. Nanomedicine has the potential to enable early detection and prevention, and to improve diagnosis, mass screening, treatment and follow-up of many diseases. From the biological standpoint, nanomaterials match the typical size of naturally occurring functional units or components of living organisms and, for this reason, enable more effective interaction with biological systems. Nanomaterials have the potential to influence the functionality and cell fate in the regeneration of organs and tissues. To this aim, nanotechnology provides an arsenal of techniques for intervening, fabricate, and modulate the environment where cells live and function. Unconventional micro- and nano-fabrication techniques allow patterning biomolecules and biocompatible materials down to the level of a few nanometer feature size. Patterning is not simply a deterministic placement of a material; in a more extended acception it allows a controlled fabrication of structures and gradients of different nature. Gradients are emerging as one of the key factors guiding cell adhesion, proliferation, migration and even differentiation in the case of stem cells. The main goal of this thesis has been to devise a nanotechnology-based strategy and tools to spatially and temporally control biologically-relevant phenomena in-vitro which are important in some fields of medical research.

The influence of film morphology on solution processed organic field-effect transistors

Organic field-effect transistors (OFETs) are becoming interesting owing to their prospective application as cheap, bendable and light weight electronic devices rnlike flexible displays. However, the bottleneck of OFETs is their typically low charge carrier mobilities. An effective and crucial route towards circumventing thisrnhurdle is the control of organic semiconductor thin film morphology which critically determine charge carrier transport. In this work, the influence of film morphologyrnis highlighted together with its impact on OFET transistor performance.

Morphology and charge transport in conjugated polymers

To assist rational compound design of organic semiconductors, two problems need to be addressed. First, the material morphology has to be known at an atomistic level. Second, with the morphology at hand, an appropriate charge transport model needs to be developed in order to link charge carrier mobility to structure.rnrnThe former can be addressed by generating atomistic morphologies using molecular dynamics simulations. However, the accessible range of time- and length-scales is limited. To overcome these limitations, systematic coarse-graining methods can be used. In the first part of the thesis, the Versatile Object-oriented Toolkit for Coarse-graining Applications is introduced, which provides a platform for the implementation of coarse-graining methods. Tools to perform Boltzmann inversion, iterative Boltzmann inversion, inverse Monte Carlo, and force-matching are available and have been tested on a set of model systems (water, methanol, propane and a single hexane chain). Advantages and problems of each specific method are discussed.rnrnIn partially disordered systems, the second issue is closely connected to constructing appropriate diabatic states between which charge transfer occurs. In the second part of the thesis, the description initially used for small conjugated molecules is extended to conjugated polymers. Here, charge transport is modeled by introducing conjugated segments on which charge carriers are localized. Inter-chain transport is then treated within a high temperature non-adiabatic Marcus theory while an adiabatic rate expression is used for intra-chain transport. The charge dynamics is simulated using the kinetic Monte Carlo method.rnrnThe entire framework is finally employed to establish a relation between the morphology and the charge mobility of the neutral and doped states of polypyrrole, a conjugated polymer. It is shown that for short oligomers, charge carrier mobility is insensitive to the orientational molecular ordering and is determined by the threshold transfer integral which connects percolating clusters of molecules that form interconnected networks. The value of this transfer integral can be related to the radial distribution function. Hence, charge mobility is mainly determined by the local molecular packing and is independent of the global morphology, at least in such a non-crystalline state of a polymer.

Morphology of leds by atomic force microscopy

The concern of this work is to present the characterization of blue emitting GaN-based LED structures by means of Atomic Force Microscopy. Here we show a comparison among the samples with different dislocation densities, in order to understand how the dislocations can affect the surface morphology. First of all we have described the current state of art of the LEDs in the present market. Thereafterwards we have mentioned in detail about the growth technique of LED structures and the methodology of the characterization employed in our thesis. Finally, we have presented the details of the results obtained on our samples studied, followed by discussions and conclusions. L'obiettivo di questa tesi é quello di presentare la caratterizzazione mediante Microscopia a Forza Atomica di strutture di LED a emissione di luce blu a base di nitruro di gallio (GaN). Viene presentato un confronto tra campioni con differente densità di dislocazioni, allo scopo di comprendere in che modo la presenza di dislocazioni influisce sulla morfologia della superficie. Innanzitutto, viene descritto il presente stato dell'arte dei LED. Successivamente, sono forniti i dettagli riguardanti la tecnica di crescita delle strutture dei LED e il metodo di caratterizzazione adottato. Infine, vengono mostrati e discussi i risultati ottenuti dallo studio dei campioni, seguiti dalle conclusioni.

Morphology control in metallocene-catalyzed polyolefin synthesis

The main aim of the work presented in this dissertation was the morphology control in metallocene-catalyzed polyolefin synthesis. This was studied by selective immobilization techniques on a variety of supports such as porous polyurethane particles (Chapter 3), electrospun fibers (Chapter 4 and 5), inorganic-organic hybrid core-shell particles (Chapter 6) and hollow silica particles (Chapter 7). Another aspect of this dissertation was modulating a catalytic activity by controlling a size of boron-based cocatalysts (Chapter 8).

Crystallization and morphology of the PLLA phase within random poly (L-lactide-ran-ɛ-caprolactone)

This work has mainly focused on the poly (L-lactide) (PLLA) which is a material for multiple applications with performances comparable to those of petrochemical polymers (PP, PS, PET, etc. ...), readily recyclable and also compostable. However, PLLA has certain shortcomings that limit its applications. It is a brittle, hard polymer with a very low elongation at break, hydrophobic, exhibits low crystallization kinetics and takes a long time to degrade. The properties of PLLA may be modified by copolymerization (random, block, and graft) of L-lactide monomers with other co-monomers. In this thesis it has been studied the crystallization and morphology of random copolymers poly (L-lactide-ran-ε-caprolactone) with different compositions of the two monomers since the physical, mechanical, optical and chemical properties of a material depend on this behavior. Thermal analyses were performed by differential scanning calorimetry (DSC) and thermogravimetry (TGA) to observe behaviors due to the different compositions of the copolymers. The crystallization kinetics and morphology of poly (L-lactide-ran-ε-caprolactone) was investigated by polarized light optical microscopy (PLOM) and differential scanning calorimetry (DSC). Their thermal behavior was observed with crystallization from melt. It was observed that with increasing amounts of PCL in the copolymer, there is a decrease of the thermal degradation. Studies on the crystallization kinetics have shown that small quantities of PCL in the copolymer increase the overall crystallization kinetics and the crystal growth rate which decreases with higher quantities of PCL.

Unraveling efficiency-limiting processes in organic solar cells by ultrafast spectroscopy - impact of chemical structure and morphology on photophysics and efficiency

Diese Arbeit widmet sich der Untersuchung der photophysikalischen Prozesse, die in Mischungen von Elektronendonoren mit Elektronenakzeptoren zur Anwendung in organischen Solarzellen auftreten. Als Elektronendonoren werden das Copolymer PBDTTT-C, das aus Benzodithiophen- und Thienothiophene-Einheiten besteht, und das kleine Molekül p-DTS(FBTTh2)2, welches Silizium-überbrücktes Dithiophen, sowie fluoriertes Benzothiadiazol und Dithiophen beinhaltet, verwendet. Als Elektronenakzeptor finden ein planares 3,4:9,10-Perylentetracarbonsäurediimid-(PDI)-Derivat und verschiedene Fullerenderivate Anwendung. PDI-Derivate gelten als vielversprechende Alternativen zu Fullerenen aufgrund der durch chemische Synthese abstimmbaren strukturellen, optischen und elektronischen Eigenschaften. Das gewichtigste Argument für PDI-Derivate ist deren Absorption im sichtbaren Bereich des Sonnenspektrums was den Photostrom verbessern kann. Fulleren-basierte Mischungen übertreffen jedoch für gewöhnlich die Effizienz von Donor-PDI-Mischungen.rnUm den Nachteil der PDI-basierten Mischungen im Vergleich zu den entsprechenden Fulleren-basierten Mischungen zu identifizieren, werden die verschiedenen Donor-Akzeptor-Kombinationen auf ihre optischen, elektronischen und strukturellen Eigenschaften untersucht. Zeitaufgelöste Spektroskopie, vor allem transiente Absorptionsspektroskopie (TA), wird zur Analyse der Ladungsgeneration angewendet und der Vergleich der Donor-PDI Mischfilme mit den Donor-Fulleren Mischfilmen zeigt, dass die Bildung von Ladungstransferzuständen einen der Hauptverlustkanäle darstellt.rnWeiterhin werden Mischungen aus PBDTTT-C und [6,6]-Phenyl-C61-buttersäuremethylesther (PC61BM) mittels TA-Spektroskopie auf einer Zeitskala von ps bis µs untersucht und es kann gezeigt werden, dass der Triplettzustand des Polymers über die nicht-geminale Rekombination freier Ladungen auf einer sub-ns Zeitskala bevölkert wird. Hochentwickelte Methoden zur Datenanalyse, wie multivariate curve resolution (MCR), werden angewendet um überlagernde Datensignale zu trennen. Zusätzlich kann die Regeneration von Ladungsträgern durch Triplett-Triplett-Annihilation auf einer ns-µs Zeitskala gezeigt werden. Darüber hinaus wird der Einfluss des Lösungsmitteladditivs 1,8-Diiodooctan (DIO) auf die Leistungsfähigkeit von p-DTS(FBTTh2)2:PDI Solarzellen untersucht. Die Erkenntnisse von morphologischen und photophysikalischen Experimenten werden kombiniert, um die strukturellen Eigenschaften und die Photophysik mit den relevanten Kenngrößen des Bauteils in Verbindung zu setzen. Zeitaufgelöste Photolumineszenzmessungen (time-resolved photoluminescence, TRPL) zeigen, dass der Einsatz von DIO zu einer geringeren Reduzierung der Photolumineszenz führt, was auf eine größere Phasentrennung zurückgeführt werden kann. Außerdem kann mittels TA Spektroskopie gezeigt werden, dass die Verwendung von DIO zu einer verbesserten Kristallinität der aktiven Schicht führt und die Generation freier Ladungen fördert. Zur genauen Analyse des Signalzerfalls wird ein Modell angewendet, das den gleichzeitigen Zerfall gebundener CT-Zustände und freier Ladungen berücksichtigt und optimierte Donor-Akzeptor-Mischungen zeigen einen größeren Anteil an nicht-geminaler Rekombination freier Ladungsträger.rnIn einer weiteren Fallstudie wird der Einfluss des Fullerenderivats, namentlich IC60BA und PC71BM, auf die Leistungsfähigkeit und Photophysik der Solarzellen untersucht. Eine Kombination aus einer Untersuchung der Struktur des Dünnfilms sowie zeitaufgelöster Spektroskopie ergibt, dass Mischungen, die ICBA als Elektronenakzeptor verwenden, eine schlechtere Trennung von Ladungstransferzuständen zeigen und unter einer stärkeren geminalen Rekombination im Vergleich zu PCBM-basierten Mischungen leiden. Dies kann auf die kleinere Triebkraft zur Ladungstrennung sowie auf die höhere Unordnung der ICBA-basierten Mischungen, die die Ladungstrennung hemmen, zurückgeführt werden. Außerdem wird der Einfluss reiner Fullerendomänen auf die Funktionsfähigkeit organischer Solarzellen, die aus Mischungen des Thienothienophen-basierenden Polymers pBTTT-C14 und PC61BM bestehen, untersucht. Aus diesem Grund wird die Photophysik von Filmen mit einem Donor-Akzeptor-Mischungsverhältnis von 1:1 sowie 1:4 verglichen. Während 1:1-Mischungen lediglich eine co-kristalline Phase, in der Fullerene zwischen den Seitenketten von pBTTT interkalieren, zeigen, resultiert der Überschuss an Fulleren in den 1:4-Proben in der Ausbildung reiner Fullerendomänen zusätzlich zu der co kristallinen Phase. Transiente Absorptionsspektroskopie verdeutlicht, dass Ladungstransferzustände in 1:1-Mischungen hauptsächlich über geminale Rekombination zerfallen, während in 1:4 Mischungen ein beträchtlicher Anteil an Ladungen ihre wechselseitige Coulombanziehung überwinden und freie Ladungsträger bilden kann, die schließlich nicht-geminal rekombinieren.

Early effects of carbachol on the morphology of motor endplates of mammalian skeletal muscle fibers

Long-term disturbance of the calcium homeostasis of motor endplates (MEPs) causes necrosis of muscle fibers. The onset of morphological changes in response to this disturbance, particularly in relation to the fiber type, is presently unknown. Omohyoid muscles of mice were incubated for 1-30 minutes in 0.1 mM carbachol, an acetylcholine agonist that causes an inward calcium current. In these muscles, the structural changes of the sarcomeres and the MEP sarcoplasm were evaluated at the light- and electron-microscopic level. Predominantly in type I fibers, carbachol incubation resulted in strong contractures of the sarcomeres underlying the MEPs. Owing to these contractures, the usual beret-like form of the MEP-associated sarcoplasm was deformed into a mushroom-like body. Consequently, the squeezed MEPs partially overlapped the adjacent muscle fiber segments. There are no signs of contractures below the MEPs if muscles were incubated in carbachol in calcium-free Tyrode's solution. Carbachol induced inward calcium current and produced fiber-type-specific contractures. This finding points to differences in the handling of calcium in MEPs. Possible mechanisms for these fiber-type-specific differences caused by carbachol-induced calcium entry are assessed.