Probiotic yogurts manufactured with increased glucose oxidase levels: Postacidification, proteolytic patterns, survival of probiotic microorganisms, production of organic acid and aroma compounds

We investigated the effect of increased glucose oxidase concentration as a technological option to decrease oxidative stress during the processing of probiotic yogurts. Probiotic yogurts were produced with increased concentrations of glucose oxidase (0, 250, 500, 750, or 1,000 mg/kg) and submitted to physicochemical and microbiological analysis at 1, 15, and 30 d of refrigerated storage. Higher concentrations of glucose oxidase (750 and 1,000 mg/kg) and a longer storage time were found to have an influence on the characteristics of the probiotic yogurt, contributing to more extensive post-acidification, an increase in the dissolved oxygen level, and higher proteolysis. In addition, increased production of aroma compounds (diacetyl and acetaldehyde) and organic acids (mainly lactic acid) and a decrease in the probiotic bacteria count were reported. The use of glucose oxidase was a feasible option to minimize oxidative stress in probiotic yogurts. However, supplementation with excessive amounts of the enzyme may be ineffective, because insufficient substrate (glucose) is present for its action. Consumer tests should be performed to evaluate changes in the sensory attributes of the probiotic yogurts with increased supplementation of glucose oxidase. In addition, packaging systems with different permeability to oxygen should be evaluated.

Optical chemical sensors using polythiophene derivatives as active layer for detection of volatile organic compounds

Several studies on polythiophene gas sensors, based mainly on electrochemical and gravimetric principles can be found in the literature. However, other principles of gas detection, such as optical and thermal, are still little studied. Optical sensing is suitable for remote detection and offers great versatility at low cost. Here,we report on the use of thin films of seven polythiophene derivatives as active layer in optical sensors for the detection of six volatile organic compounds (n-hexane, toluene, tetrahydrofuran, chloroform, dichloromethane and methanol) and water vapor, in concentration range of 500-30,000 ppm. The results showed that it is possible to use different polythiophene derivatives to differentiate VOCs by optical sensing. Differentiation can be performed based on the presence or not of response to an analyte and the sensitivity value of the sensors for the analytes. Another important feature is the lack of the effect of humidity on the response of most films, which could be a major drawback in the application of these sensors. (C) 2011 Elsevier B.V. All rights reserved.

Polymeric Nanoparticles as Oral Delivery Systems for Encapsulation and Release of Polyphenolic Compounds: Impact on Quercetin Antioxidant Activity & Bioaccessibility

A delivery system containing polymeric (Eudragit) nanoparticles has been developed for encapsulation and controlled release of bioactive flavonoids (quercetin). Nanoparticles were fabricated using a solvent displacement method. Particle size, morphology, and charge were measured by light scattering, electron microscopy and zeta-potential. Encapsulation efficiency (EE) and release profiles were determined using electrochemical methods. Molecular interactions within the particle matrix were characterized by X-ray diffraction, differential scanning calorimetry, and infrared spectroscopy. Antioxidant properties of free and encapsulated quercetin were analyzed by TBARS and fluorescence spectroscopy. Bioaccessibility of quercetin was evaluated using an in vitro digestion model. Relatively small (d a parts per thousand aEuro parts per thousand 370 nm) anionic polymeric nanoparticles were formed containing quercetin in a non-crystalline form (EE a parts per thousand aEuro parts per thousand 67 %). The main interaction between quercetin and Eudragit was hydrogen bonding. Encapsulated quercetin remained stable during 6 months storage and maintained its antioxidant activity. Quercetin bioaccessibility within simulated small intestinal conditions was improved by encapsulation. The knowledge obtained from this study will facilitate the rational design and fabrication of polymeric nanoparticles as oral delivery systems for encapsulation, protection, and release of bioactive compounds.

OSCILLATORY DYNAMICS IN SYSTEMS CONTAINING BROMATE AND 1,4-CYCLOHEXANEDIONE IN ACIDIC MEDIA. I. THE EFFECT OF TEMPERATURE.

OSCILLATORY DYNAMICS IN SYSTEMS CONTAINING BROMATE AND 1,4-CYCLOHEXANEDIONE IN ACIDIC MEDIA. I. THE EFFECT OF TEMPERATURE. We present in this work the influence of temperature on the dynamics of homogeneous chemical systems containing bromate and 1,4-cyclohexanedione (1,4-CHD) in acidic media. In particular, the following systems were studied: bromate/1,4-CHD/acid, bromate/1,4-CHD/ferroin/acid and bromate/1,4-CHD/trisbipyridine ruthenium/acid. Investigations were carried out by means of an electrochemical probe, at five temperatures between 5 and 45 degrees C. Activation energies (E-a) were estimated in different ways for the pre-oscillatory and oscillatory regimes. In any case, the E-a was found to depend on the catalyst, composition and initial concentrations. In addition, it was observed that ferroin and trisbipyridine ruthenium act as catalysts only during the transition between the induction period and oscillatory regime.

Effects of early compost application on no-till organic soybean

Weed control has always been an important issue in agriculture. With the advent of no-till systems, soil erosion was reduced but herbicide use was increased. Organic no-till systems try to adjust reduced erosion to the no use of herbicides. Nevertheless, this adjustment is limited by the cost of mechanical weed control. This cost may be reduced by improved cultural weed control with cover crops mulches. In this paper we report a study on the application of compost manure on an oats winter cover crop, preceding soybean, instead of on the soybean summer crop. Treatments comprised a control without compost manure, and compost manure doses of 4 and 8 Mg ha-1 applied either on oats in winter or soybean in summer, organized in a randomized block design, with five replications. In summer, plots were split into weed-controlled or not controlled subplots. The timing of application and the manure doses did not affect the oats biomass or the soybean performance. However, in summer, without water stress, the application of manure at 8 Mg ha-1 directly on soybean has reduced weed biomass in this crop.

An evaluation of the distributions of polychlorinated biphenyls and organic matter in coastal sediments

The objective of this thesis is to improve the understanding of what processes and mechanism affects the distribution of polychlorinated biphenyls (PCBs) and organic carbon in coastal sediments. Because of the strong association of hydrophobic organic contaminants (HOCs) such as PCBs with organic matter in the aquatic environment, these two entities are naturally linked. The coastal environment is the most complex and dynamic part of the ocean when it comes to both cycling of organic matter and HOCs. This environment is characterised by the largest fluxes and most diverse sources of both entities. A wide array of methods was used to study these processes throughout this thesis. In the field sites in the Stockholm archipelago of the Baltic proper, bottom sediments and settling particulate matter were retrieved using sediment coring devices and sediment traps from morphometrically and seismically well-characterized locations. In the laboratory, the samples have been analysed for PCBs, stable carbon isotope ratios, carbon-nitrogen atom ratios as well as standard sediment properties. From the fieldwork in the Stockholm Archipelago and the following laboratory work it was concluded that the inner Stockholm archipelago has a low (≈ 4%) trapping efficiency for freshwater-derived organic carbon. The corollary is a large potential for long-range waterborne transport of OC and OC-associated nutrients and hydrophobic organic pollutants from urban Stockholm to more pristine offshore Baltic Sea ecosystems. Theoretical work has been carried out using Geographical Information Systems (GIS) and statistical methods on a database of 4214 individual sediment samples, each with reported individual PCB congener concentrations. From this work it was concluded that the continental shelf sediments are key global inventories and ultimate sinks of PCBs. Depending on congener, 10-80% of the cumulative historical emissions to the environment are accounted for in continental shelf sediments. Further it was concluded that the many infamous and highly contaminated surface sediments of urban harbours and estuaries of contaminated rivers cannot be of importance as a secondary source to sustain the concentrations observed in remote sediments. Of the global shelf PCB inventory < 1% are in sediments near population centres while ≥ 90% is in remote areas (> 10 km from any dwellings). The remote sub-basin of the North Atlantic Ocean contains approximately half of the global shelf sediment inventory for most of the PCBs studied.

Transformations of bridging ligands in diiron complexes: unconventional routes to new functionalized multisite bound organic frames

The main scope of this Ph.D. thesis has concerned the possible transformations of bridging ligands in diiron complexes, in order to explore unconventional routes to the synthesis of new functionalized multisite bound organic frames. The results achieved during the Ph.D. can be summarized in the following points: 1) We have extended the assembling between small unsaturated molecules and bridging carbyne ligands in diiron complexes to other species. In particular, we have investigated the coupling between olefins and thiocarbyne, leading to the synthesis of thioallylidene bridging diiron complexes. Then, we have extended the study to the coupling between olefins and aminocarbyne. This result shows that the coupling between activated olefins and heteroatom substituted bridging carbynes has a general character. 2) As we have shown, the coupling of bridging alkylidyne ligands with alkynes and alkenes provides excellent routes to the synthesis of bridging C3 hydrocarbyl ligands. As a possible extension of these results we have examined the synthesis of C4 bridging frames through the combination of bridging alkylidynes with allenes. Also in this case the reaction has a general character. 3) Diiron complexes bearing bridging functionalized C3 organic frames display the presence of donor atoms, such as N and S, potentially able to coordinate unsaturated metal fragments. Thus, we have studied the possibility for these systems to act as ‘organometallic ligands’, in particular towards Pd and Rh. 4) The possibility of releasing the organic frame from the bridging coordination appears particularly appealing in the direction of a metal-assisted organic synthesis. Within this field, we have investigated the possibility of involving the C3 bridging ligand in cycloaddition reactions with alkynes, with the aim of generating variously functionalized five-membered cycles. The [3+2] cyclization does not lead to the complete release of the organic fragment but rather it produces its transformation into a cyclopentadienyl ring, which remains coordinated to one Fe atom. This result introduces a new approach to the formation of polyfunctionalised ferrocenes. 5) Furthermore, I have spent a research period of about six months at the Department of Inorganic Chemistry of the Barcelona University, under the supervision of Prof. Concepción López, with the aim of studying the chemistry of polydentate ferrocenyl ligands and their use in organometallic synthesis.

Innovative Homogeneous and Heterogeneous Systems for Electrochemically Generated Luminescence Investigations: Towards One-Dimensional ECL

My research PhD work is focused on the Electrochemically Generated Luminescence (ECL) investigation of several different homogeneous and heterogeneous systems. ECL is a redox induced emission, a process whereby species, generated at electrodes, undergo a high-energy electron transfer reaction to form excited states that emit light. Since its first application, the ECL technique has become a very powerful analytical tool and has widely been used in biosensor transduction. ECL presents an intrinsically low noise and high sensitivity; moreover, the electrochemical generation of the excited state prevents scattering of the light source: for all these characteristics, it is an elective technique for ultrasensitive immunoassay detection. The majority of ECL systems involve species in solution where the emission occurs in the diffusion layer near to the electrode surface. However, over the past few years, an intense research has been focused on the ECL generated from species constrained on the electrode surface. The aim of my work is to study the behavior of ECL-generating molecular systems upon the progressive increase of their spatial constraints, that is, passing from isolated species in solution, to fluorophores embedded within a polymeric film and, finally, to patterned surfaces bearing “one-dimensional” emitting spots. In order to describe these trends, I use different “dimensions” to indicate the different classes of compounds. My thesis was mostly developed in the electrochemistry group of Bologna with the supervision of Prof Francesco Paolucci and Dr Massimo Marcaccio. With their help and also thanks to their long experience in the molecular and supramolecular ECL fields and in the surface investigations using scanning probe microscopy techniques, I was able to obtain the results herein described. Moreover, during my research work, I have established a new collaboration with the group of Nanobiotechnology of Prof. Robert Forster (Dublin City University) where I spent a research period. Prof. Forster has a broad experience in the biomedical field, especially he focuses his research on film surfaces biosensor based on the ECL transduction. This thesis can be divided into three sections described as follows: (i) in the fist section, homogeneous molecular and supramolecular ECL-active systems, either organic or inorganic species (i.e., corannulene, dendrimers and iridium metal complex), are described. Driving force for this kind of studies includes the search for new luminophores that display on one hand higher ECL efficiencies and on the other simple mechanisms for modulating intensity and energy of their emission in view of their effective use in bioconjugation applications. (ii) in the second section, the investigation of some heterogeneous ECL systems is reported. Redox polymers comprising inorganic luminophores were described. In such a context, a new conducting platform, based on carbon nanotubes, was developed aimed to accomplish both the binding of a biological molecule and its electronic wiring to the electrode. This is an essential step for the ECL application in the field of biosensors. (iii) in the third section, different patterns were produced on the electrode surface using a Scanning Electrochemical Microscopy. I developed a new methods for locally functionalizing an inert surface and reacting this surface with a luminescent probe. In this way, I successfully obtained a locally ECL active platform for multi-array application.

Modeling, design and experimental characterization of Micro-Electro-Mechanical-Systems for gas chromatographic applications

Design parameters, process flows, electro-thermal-fluidic simulations and experimental characterizations of Micro-Electro-Mechanical-Systems (MEMS) suited for gas-chromatographic (GC) applications are presented and thoroughly described in this thesis, whose topic belongs to the research activities the Institute for Microelectronics and Microsystems (IMM)-Bologna is involved since several years, i.e. the development of micro-systems for chemical analysis, based on silicon micro-machining techniques and able to perform analysis of complex gaseous mixtures, especially in the field of environmental monitoring. In this regard, attention has been focused on the development of micro-fabricated devices to be employed in a portable mini-GC system for the analysis of aromatic Volatile Organic Compounds (VOC) like Benzene, Toluene, Ethyl-benzene and Xylene (BTEX), i.e. chemical compounds which can significantly affect environment and human health because of their demonstrated carcinogenicity (benzene) or toxicity (toluene, xylene) even at parts per billion (ppb) concentrations. The most significant results achieved through the laboratory functional characterization of the mini-GC system have been reported, together with in-field analysis results carried out in a station of the Bologna air monitoring network and compared with those provided by a commercial GC system. The development of more advanced prototypes of micro-fabricated devices specifically suited for FAST-GC have been also presented (silicon capillary columns, Ultra-Low-Power (ULP) Metal OXide (MOX) sensor, Thermal Conductivity Detector (TCD)), together with the technological processes for their fabrication. The experimentally demonstrated very high sensitivity of ULP-MOX sensors to VOCs, coupled with the extremely low power consumption, makes the developed ULP-MOX sensor the most performing metal oxide sensor reported up to now in literature, while preliminary test results proved that the developed silicon capillary columns are capable of performances comparable to those of the best fused silica capillary columns. Finally, the development and the validation of a coupled electro-thermal Finite Element Model suited for both steady-state and transient analysis of the micro-devices has been described, and subsequently implemented with a fluidic part to investigate devices behaviour in presence of a gas flowing with certain volumetric flow rates.

Discotic materials for organic electronics

Die Kontrolle der ausgeprägten Aggregationsfähigkeit von alkylsubstituierten Hexa-peri-hexabenzocoronenen (HBC) wurde durch die Reduktion der intermolekularen Wechselwirkungen erreicht. Sterisch anspruchsvolle, verzweigte Alkylketten, mit einem Verzweigungspunkt naher des aromatischen Kerns, wurden in die Corona der aromatischen Scheiben eingebracht und verleihen den Derivaten Schmelzbarkeit ohne thermische Zersetzung. Dies erlaubte eine kostengünstige Verarbeitungstechniken direkt aus der Schmelze wie z.B. Zonenschmelzen, um uniaxial organisierte makroskopische Filme zu erhalten. Abhängig von dem sterischen Anspruch, der durch die Seitenkette erzeugt wird, wurden unterschiedliche molekulare Orientierungen auf Oberflächen erhalten, was eine wichtige Voraussetzung ist, um diskotische Materialien in elektronische Bauteile zu implementieren. Eine weitere Voraussetzung sind hohe Ladungsträgerbeweglichkeiten und Ladungsträgerlebenszeiten in den Halbleitermaterialien, die mit time-resolved pulse-radiolysis microwave conductivity (TR-PRMC) und time-of-flight (TOF) auch für die synthetisieren Materialien bestimmt wurden. Die neuen Materialien zeigten bereits in organischen Solarzellen gute Leistungen. Den Einfluss des Perimeters auf die elektronischen Eigenschaften der polyzyklischen aromatischen Kohlenwasserstoffe (PAKs) wurde theoretisch vorhergesagt und in dieser Arbeit durch die Synthese einer homologe Serie von PAKs experimentell bestätigt. Geht man von der „arm-chair“ Peripherie des HBC sukzessive zu einer partiellen „zickzack“ Peripherie, so findet man eine Abhängigkeit der elektronischen Banden von Symmetrie und Größe des aromatischen Systems. Die spontan ausgebildete Überstruktur dieser Derivate zeigte eine Abhängigkeit von Substitutionsmuster und der Natur der Alkylketten. Zusammenfassend wurden neben der Synthese von neuartigen Materialien für den Einsatz in der organischen Elektronik Synthesen entwickelt, die eine vereinfachte Funktionalisierung von ausgedehnten PAKs ermöglicht. Diese Konzepte erlauben eine Justierung der molekularen und supramolekularen Eigenschaften, eines der wichtigsten Voraussetzungen für den Einsatz von Materialien in elektronischen Bauelementen.

Synthetical engineering of supramolecular properties of large polycyclic aromatic hydrocarbons

An important property for devices is the charge-carrier mobility values for discotic organic materials like hexa-peri-hexabenzocoronenes. A close relation exists between the degree of their columnar self-arrangement of the molecules and their mobilities. Within this first step an induction of a higher order via hydrogen-bonding was considered, which mainly pointed towards the improvement of the intracolumnar stacking of the materials. For the analytics a broad range of methods was used including differential scanning calorimetry (DSC), wide-angle X-ray diffractometry (WAXS), solid-state NMR spectroscopy and scanning tunneling microscopy (STM). Indeed, a specific influence of the hydrogen-bonds could be identified, although in several cases by the cost of a severe reduction of solubility and processability. This effect was dampened by the addition of a long alkyl chain next to the hydrogen-bond exerting functional group, which resulted in an improved columnar arrangement by retention of processability. In contrast to the before mentioned example of inducing a higher intracolumnar order by hydrogen-bonding, the focus was also be set upon larger aromatic systems. The charge-carrier mobility is also in close relation to the size of the aromatic core and larger π-areas are expected to lead to improved mobilities. For photovoltaic applications a high extinction coefficient over a broad range of the spectrum is favorable, which can also be achieved by enlarging the aromatic core component. In addition the stronger π-interactions between the aromatic core components should yield an improved columnar stability and order. However the strengthening of the π-interactions between the aromatic core components led to a reduction of the solubility and the processability due to the stronger aggregation of the molecules. This required the introduction of efficiently solubilizing features in terms of long alkyl chains in the corona of the aromatic entity, in combination of a distortion of the aromatic core moiety by bulky tert-butyl groups. By this approach not only the processing and cleaning of the materials with standard laboratory techniques became possible, but moreover the first structure-rich UV/vis and a resolved 1H-NMR spectra for an aromatic system two times larger than hexa-peri-hexabenzocoronene were recorded. The bulk properties in an extruded fiber as well as on the surface showed a columnar self-assembly including a phase in which a homeotropic alignment on a substrate was observed, which turns the material into an interesting candidate for future applications in electronic devices.

Pratiche del possibile: i Participatory Guarantee Systems e le scelte d'acquisto del consumatore brasiliano

Negli ultimi anni, parallelamente all’espansione del settore biologico, si è assistito a un crescente interesse per i modelli alternativi di garanzia dell’integrità e della genuinità dei prodotti biologici. Gruppi di piccoli agricoltori di tutto il mondo hanno iniziato a sviluppare approcci alternativi per affrontare i problemi connessi alla certificazione di terza parte. Queste pratiche sono note come Sistemi di Garanzia Partecipativa (PGS). Tali modelli: (i) si basano sugli standard di certificazione biologica dell’IFOAM, (ii) riguardano il complesso dei produttori di una comunità rurale, (iii) comportano l’inclusione di una grande varietà di attori e (iv) hanno lo scopo di ridurre al minimo burocrazia e costi semplificando le procedure di verifica e incorporando un elemento di educazione ambientale e sociale sia per i produttori sia per i consumatori. Gli obiettivi di questo lavoro di ricerca: • descrivere il funzionamento dei sistemi di garanzia partecipativa; • indicare i vantaggi della loro adozione nei Paesi in via di sviluppo e non; • illustrare il caso della Rede Ecovida de Agroecologia (Brasile); • offrire uno spunto di riflessione che riguarda il consumatore e la relativa fiducia nel modello PGS. L’impianto teorico fa riferimento alla Teoria delle Convenzioni. Sulla base del quadro teorico è stato costruito un questionario per i consumatori con lo scopo di testare l’appropriatezza delle ipotesi teoriche. I risultati finali riguardano la stima del livello di conoscenza attuale, la fiducia e la volontà d’acquisto dei prodotti PGS da parte dei consumatori nelle aree considerate. Sulla base di questa ricerca sarà possibile adattare ed esportare il modello empirico in altri paesi che presentano economie diverse per cercare di comprendere il potenziale campo di applicazione dei sistemi di garanzia partecipativa.

Diffusion in polymer systems studied by fluorescence correlation spectroscopy

Fluorescence correlation spectroscopy (FCS) is a powerful technique to determine the diffusion of fluorescence molecules in various environments. The technique is based on detecting and analyzing the fluctuation of fluorescence light emitted by fluorescence species diffusing through a small and fixed observation volume, formed by a laser focused into the sample. Because of its great potential and high versatility in addressing the diffusion and transport properties in complex systems, FCS has been successfully applied to a great variety of systems. In my thesis, I focused on the application of FCS to study the diffusion of fluorescence molecules in organic environments, especially in polymer melts. In order to examine our FCS setup and a developed measurement protocol, I first utilized FCS to measure tracer diffusion in polystyrene (PS) solutions, for which abundance data exist in the literature. I studied molecular and polymeric tracer diffusion in polystyrene solutions over a broad range of concentrations and different tracer and matrix molecular weights (Mw). Then FCS was further established to study tracer dynamics in polymer melts. In this part I investigated the diffusion of molecular tracers in linear flexible polymer melts [polydimethylsiloxane (PDMS), polyisoprene (PI)], a miscible polymer blend [PI and poly vinyl ethylene (PVE)], and star-shaped polymer [3-arm star polyisoprene (SPI)]. The effects of tracer sizes, polymer Mw, polymer types, and temperature on the diffusion coefficients of small tracers were discussed. The distinct topology of the host polymer, i.e. star polymer melt, revealed the notably different motion of the small tracer, as compared to its linear counterpart. Finally, I emphasized the advantage of the small observation volume which allowed FCS to investigate the tracer diffusions in heterogeneous systems; a swollen cross-linked PS bead and silica inverse opals, where high spatial resolution technique was required.

Simulations of charge transport in organic compounds

To aid the design of organic semiconductors, we study the charge transport properties of organic liquid crystals, i.e. hexabenzocoronene and carbazole macrocycle, and single crystals, i.e. rubrene, indolocarbazole and benzothiophene derivatives (BTBT, BBBT). The aim is to find structure-property relationships linking the chemical structure as well as the morphology with the bulk charge carrier mobility of the compounds. To this end, molecular dynamics (MD) simulations are performed yielding realistic equilibrated morphologies. Partial charges and molecular orbitals are calculated based on single molecules in vacuum using quantum chemical methods. The molecular orbitals are then mapped onto the molecular positions and orientations, which allows calculation of the transfer integrals between nearest neighbors using the molecular orbital overlap method. Thus we obtain realistic transfer integral distributions and their autocorrelations. In case of organic crystals the differences between two descriptions of charge transport, namely semi-classical dynamics (SCD) in the small polaron limit and kinetic Monte Carlo (KMC) based on Marcus rates, are studied. The liquid crystals are investigated solely in the hopping limit. To simulate the charge dynamics using KMC, the centers of mass of the molecules are mapped onto lattice sites and the transfer integrals are used to compute the hopping rates. In the small polaron limit, where the electronic wave function is spread over a limited number of neighboring molecules, the Schroedinger equation is solved numerically using a semi-classical approach. The results are compared for the different compounds and methods and, where available, with experimental data. The carbazole macrocycles form columnar structures arranged on a hexagonal lattice with side chains facing inwards, so columns can closely approach each other allowing inter-columnar and thus three-dimensional transport. When taking only intra-columnar transport into account, the mobility is orders of magnitude lower than in the three-dimensional case. BTBT is a promising material for solution-processed organic field-effect transistors. We are able to show that, on the time-scales of charge transport, static disorder due to slow side chain motions is the main factor determining the mobility. The resulting broad transfer integral distributions modify the connectivity of the system but sufficiently many fast percolation paths remain for the charges. Rubrene, indolocarbazole and BBBT are examples of crystals without significant static disorder. The high mobility of rubrene is explained by two main features: first, the shifted cofacial alignment of its molecules, and second, the high center of mass vibrational frequency. In comparsion to SCD, only KMC based on Marcus rates is capable of describing neighbors with low coupling and of taking static disorder into account three-dimensionally. Thus it is the method of choice for crystalline systems dominated by static disorder. However, it is inappropriate for the case of strong coupling and underestimates the mobility of well-ordered crystals. SCD, despite its one-dimensionality, is valuable for crystals with strong coupling and little disorder. It also allows correct treatment of dynamical effects, such as intermolecular vibrations of the molecules. Rate equations are incapable of this, because simulations are performed on static snapshots. We have thus shown strengths and weaknesses of two state of the art models used to study charge transport in organic compounds, partially developed a program to compute and visualize transfer integral distributions and other charge transport properties, and found structure-mobility relations for several promising organic semiconductors.

Interplay of pi–pi stacking and hydrogen bonding in conjugated supramolecular systems studied by solid-state NMR

In this work supramolecular organic systems based on rigid pi-conjugated building blocks and flexible side chains were studied via solid-state NMR spectroscopy. Specifically, these studies focussed on phenylene ethynylene based macrocycles, polymer systems including polythiophenes, and rod-coil copolymers of oligo(p-benzamide) and poly(ethylene glycol). All systems were studied in terms of the local order and mobility. The central topic of this dissertation was to elucidate the role of the flexible side chains in interplay of different non-covalent interactions, like pi-pi-stacking and hydrogen bonding.Combining the results of this work, it can be concluded that the ratio of the rigid block and the attached alkyl side chains can be crucial for the design of an ordered pi-conjugated supramolecular system. Through alkyl side chains, it is also possible to introduce liquid-crystalline phases in the system, which can foster the local order of the system. Moreover in the studied system longer, unbranched alkyl side chains are better suited to stabilize the corresponding aggregation than shorter, branched ones.The combination of non-covalent interactions such as pi-pi-stacking and hydrogen bonding play an important role for structure formation. However, the effect of pi-pi-stacking interaction is much weaker than the effect of hydrogen bonding and is only observed in systems with a suitable local order. Hence, they are often not strong enough to control the local order. In contrast, hydrogen bonds predominantly influence the structural organization and packing. In comparison the size of the alkyl side chains is only of minor importance. The suppression of certain hydrogen bonds can lead to completely different structures and can induce a specific aggregation behavior. Thus, for the design of a supramolecular ordered system the presence of hydrogen bonding efficiently stabilizes the corresponding structure, but the ratio of hydrogen bond forming groups should be kept low to be able to influence the structure selectively.