Caratterizzazione del legame di molecole di interesse farmaceutico alla sieroalbumina umana mediante biocromatografia e dicroismo circolare

Negli ultimi anni, un crescente numero di studiosi ha focalizzato la propria attenzione sullo sviluppo di strategie che permettessero di caratterizzare le proprietà ADMET dei farmaci in via di sviluppo, il più rapidamente possibile. Questa tendenza origina dalla consapevolezza che circa la metà dei farmaci in via di sviluppo non viene commercializzato perché ha carenze nelle caratteristiche ADME, e che almeno la metà delle molecole che riescono ad essere commercializzate, hanno comunque qualche problema tossicologico o ADME [1]. Infatti, poco importa quanto una molecola possa essere attiva o specifica: perché possa diventare farmaco è necessario che venga ben assorbita, distribuita nell’organismo, metabolizzata non troppo rapidamente, ne troppo lentamente e completamente eliminata. Inoltre la molecola e i suoi metaboliti non dovrebbero essere tossici per l’organismo. Quindi è chiaro come una rapida determinazione dei parametri ADMET in fasi precoci dello sviluppo del farmaco, consenta di risparmiare tempo e denaro, permettendo di selezionare da subito i composti più promettenti e di lasciar perdere quelli con caratteristiche negative. Questa tesi si colloca in questo contesto, e mostra l’applicazione di una tecnica semplice, la biocromatografia, per caratterizzare rapidamente il legame di librerie di composti alla sieroalbumina umana (HSA). Inoltre mostra l’utilizzo di un’altra tecnica indipendente, il dicroismo circolare, che permette di studiare gli stessi sistemi farmaco-proteina, in soluzione, dando informazioni supplementari riguardo alla stereochimica del processo di legame. La HSA è la proteina più abbondante presente nel sangue. Questa proteina funziona da carrier per un gran numero di molecole, sia endogene, come ad esempio bilirubina, tiroxina, ormoni steroidei, acidi grassi, che xenobiotici. Inoltre aumenta la solubilità di molecole lipofile poco solubili in ambiente acquoso, come ad esempio i tassani. Il legame alla HSA è generalmente stereoselettivo e ad avviene a livello di siti di legame ad alta affinità. Inoltre è ben noto che la competizione tra farmaci o tra un farmaco e metaboliti endogeni, possa variare in maniera significativa la loro frazione libera, modificandone l’attività e la tossicità. Per queste sue proprietà la HSA può influenzare sia le proprietà farmacocinetiche che farmacodinamiche dei farmaci. Non è inusuale che un intero progetto di sviluppo di un farmaco possa venire abbandonato a causa di un’affinità troppo elevata alla HSA, o a un tempo di emivita troppo corto, o a una scarsa distribuzione dovuta ad un debole legame alla HSA. Dal punto di vista farmacocinetico, quindi, la HSA è la proteina di trasporto del plasma più importante. Un gran numero di pubblicazioni dimostra l’affidabilità della tecnica biocromatografica nello studio dei fenomeni di bioriconoscimento tra proteine e piccole molecole [2-6]. Il mio lavoro si è focalizzato principalmente sull’uso della biocromatografia come metodo per valutare le caratteristiche di legame di alcune serie di composti di interesse farmaceutico alla HSA, e sul miglioramento di tale tecnica. Per ottenere una miglior comprensione dei meccanismi di legame delle molecole studiate, gli stessi sistemi farmaco-HSA sono stati studiati anche con il dicroismo circolare (CD). Inizialmente, la HSA è stata immobilizzata su una colonna di silice epossidica impaccata 50 x 4.6 mm di diametro interno, utilizzando una procedura precedentemente riportata in letteratura [7], con alcune piccole modifiche. In breve, l’immobilizzazione è stata effettuata ponendo a ricircolo, attraverso una colonna precedentemente impaccata, una soluzione di HSA in determinate condizioni di pH e forza ionica. La colonna è stata quindi caratterizzata per quanto riguarda la quantità di proteina correttamente immobilizzata, attraverso l’analisi frontale di L-triptofano [8]. Di seguito, sono stati iniettati in colonna alcune soluzioni raceme di molecole note legare la HSA in maniera enantioselettiva, per controllare che la procedura di immobilizzazione non avesse modificato le proprietà di legame della proteina. Dopo essere stata caratterizzata, la colonna è stata utilizzata per determinare la percentuale di legame di una piccola serie di inibitori della proteasi HIV (IPs), e per individuarne il sito(i) di legame. La percentuale di legame è stata calcolata attraverso il fattore di capacità (k) dei campioni. Questo parametro in fase acquosa è stato estrapolato linearmente dal grafico log k contro la percentuale (v/v) di 1-propanolo presente nella fase mobile. Solamente per due dei cinque composti analizzati è stato possibile misurare direttamente il valore di k in assenza di solvente organico. Tutti gli IPs analizzati hanno mostrato un’elevata percentuale di legame alla HSA: in particolare, il valore per ritonavir, lopinavir e saquinavir è risultato maggiore del 95%. Questi risultati sono in accordo con dati presenti in letteratura, ottenuti attraverso il biosensore ottico [9]. Inoltre, questi risultati sono coerenti con la significativa riduzione di attività inibitoria di questi composti osservata in presenza di HSA. Questa riduzione sembra essere maggiore per i composti che legano maggiormente la proteina [10]. Successivamente sono stati eseguiti degli studi di competizione tramite cromatografia zonale. Questo metodo prevede di utilizzare una soluzione a concentrazione nota di un competitore come fase mobile, mentre piccole quantità di analita vengono iniettate nella colonna funzionalizzata con HSA. I competitori sono stati selezionati in base al loro legame selettivo ad uno dei principali siti di legame sulla proteina. In particolare, sono stati utilizzati salicilato di sodio, ibuprofene e valproato di sodio come marker dei siti I, II e sito della bilirubina, rispettivamente. Questi studi hanno mostrato un legame indipendente dei PIs ai siti I e II, mentre è stata osservata una debole anticooperatività per il sito della bilirubina. Lo stesso sistema farmaco-proteina è stato infine investigato in soluzione attraverso l’uso del dicroismo circolare. In particolare, è stato monitorata la variazione del segnale CD indotto di un complesso equimolare [HSA]/[bilirubina], a seguito dell’aggiunta di aliquote di ritonavir, scelto come rappresentante della serie. I risultati confermano la lieve anticooperatività per il sito della bilirubina osservato precedentemente negli studi biocromatografici. Successivamente, lo stesso protocollo descritto precedentemente è stato applicato a una colonna di silice epossidica monolitica 50 x 4.6 mm, per valutare l’affidabilità del supporto monolitico per applicazioni biocromatografiche. Il supporto monolitico monolitico ha mostrato buone caratteristiche cromatografiche in termini di contropressione, efficienza e stabilità, oltre che affidabilità nella determinazione dei parametri di legame alla HSA. Questa colonna è stata utilizzata per la determinazione della percentuale di legame alla HSA di una serie di poliamminochinoni sviluppati nell’ambito di una ricerca sulla malattia di Alzheimer. Tutti i composti hanno mostrato una percentuale di legame superiore al 95%. Inoltre, è stata osservata una correlazione tra percentuale di legame è caratteristiche della catena laterale (lunghezza e numero di gruppi amminici). Successivamente sono stati effettuati studi di competizione dei composti in esame tramite il dicroismo circolare in cui è stato evidenziato un effetto anticooperativo dei poliamminochinoni ai siti I e II, mentre rispetto al sito della bilirubina il legame si è dimostrato indipendente. Le conoscenze acquisite con il supporto monolitico precedentemente descritto, sono state applicate a una colonna di silice epossidica più corta (10 x 4.6 mm). Il metodo di determinazione della percentuale di legame utilizzato negli studi precedenti si basa su dati ottenuti con più esperimenti, quindi è necessario molto tempo prima di ottenere il dato finale. L’uso di una colonna più corta permette di ridurre i tempi di ritenzione degli analiti, per cui la determinazione della percentuale di legame alla HSA diventa molto più rapida. Si passa quindi da una analisi a medio rendimento a una analisi di screening ad alto rendimento (highthroughput- screening, HTS). Inoltre, la riduzione dei tempi di analisi, permette di evitare l’uso di soventi organici nella fase mobile. Dopo aver caratterizzato la colonna da 10 mm con lo stesso metodo precedentemente descritto per le altre colonne, sono stati iniettati una serie di standard variando il flusso della fase mobile, per valutare la possibilità di utilizzare flussi elevati. La colonna è stata quindi impiegata per stimare la percentuale di legame di una serie di molecole con differenti caratteristiche chimiche. Successivamente è stata valutata la possibilità di utilizzare una colonna così corta, anche per studi di competizione, ed è stata indagato il legame di una serie di composti al sito I. Infine è stata effettuata una valutazione della stabilità della colonna in seguito ad un uso estensivo. L’uso di supporti cromatografici funzionalizzati con albumine di diversa origine (ratto, cane, guinea pig, hamster, topo, coniglio), può essere proposto come applicazione futura di queste colonne HTS. Infatti, la possibilità di ottenere informazioni del legame dei farmaci in via di sviluppo alle diverse albumine, permetterebbe un migliore paragone tra i dati ottenuti tramite esperimenti in vitro e i dati ottenuti con esperimenti sull’animale, facilitando la successiva estrapolazione all’uomo, con la velocità di un metodo HTS. Inoltre, verrebbe ridotto anche il numero di animali utilizzati nelle sperimentazioni. Alcuni lavori presenti in letteratura dimostrano l’affidabilita di colonne funzionalizzate con albumine di diversa origine [11-13]: l’utilizzo di colonne più corte potrebbe aumentarne le applicazioni.

Stereoselective Catalytic Processes for the Synthesis of Polycyclic Aromatic Compounds

In this PhD-thesis, two methodologies for enantioselective intramolecular ring closing reaction on indole cores are presented. The first methodology represents a highly stereoselective alkylation of the indole N1-nitrogen, leading to 3,4-dihydro-pyrazinoindol-1-ones – a structural class which is known for its activity on the CNS and therefore of high pharmacological interest concerning related diseases. In this approach, N-benzyl cinchona-alkaloids were used for the efficient catalysis of intramolecular aza-Michael reactions. Furthermore, computational studies in collaboration with the research group Prof. Andrea Bottoni (Department of Chemistry “G. Ciamician”, Bologna) were accomplished in order to get insight into the key interactions between catalyst and substrate, leading to enantiomeric excesses up to 91%. The results of the calculations on a model system are in accordance with the experimental results and demonstrate the high sensibility of the system towards structural modifications. The second project deals with a metal catalyzed, intramolecular Friedel-Crafts (FC)-reaction on indolyl substrates, carrying a side chain which on its behalf is furnished with an allylic alcohol unit. Allylic alcohols are part of the structural class of “π-activated alcohols” – alcohols, which are more easily activated due to the proximity to a π-unit (allyl-, propargyl-, benzyl-). The enantioselective intramolecular cyclization event is catalyzed efficiently by employment of a chiral Au(I)-catalyst, leading to 1-vinyl- or 4-vinyl-tetrahydrocarbazoles (THCs) under the formation of water as byproduct. This striking and novel process concerning the direct activation of alcohols in catalytic FC-reactions was subsequently extended to similar precursors, leading to functionalized tetrahydro-β-carbolines. These two methodologies represent highly efficient approaches towards the synthesis of scaffolds, which are of enormous pharmaceutical interest and amplify the spectra of enantioselective catalytic functionalisations of indoles.

Materiali Politiofenici Otticamente Attivi

Much effort has been devoted in the recent years to the investigation of optically active polythiophenes characterized by the presence of a chiral moiety linked to the 3-position of the aromatic ring. In addition to their potential technological applications as materials for enantioselective electrodes and membranes, chiral poly(thiophene)s offer the possibility of studying the structural changes accompanying the transition from the disordered state by following the variation of their chiroptical properties by circular dichroism (CD). In solution of a good solvent, that kind of polythiophenes doesn’t display any optical activity arising from the presence of dissymmetric conformation of the backbone, as shown by circular dichroism (CD) spectra. When the macromolecules begin to aggregate, as it occurs e.g. by addition of a poor solvent, or lowering the solution temperature, or when the macromolecules are assembled in the solid state as thin films obtained by solution casting or spin coating, significant CD bands are observed in the spectral region related to the electronic absorptions of the aromatic polythiophene chromophore. These CD bands are indicative of a chiral macromolecule arrangement of one prevailing chirality. The synthesis of -substituted polythiophenes can be carried out starting from the corresponding -substituted mono- or oligomeric thiophenic monomers under regioselective or regiospecific conditions in order to minimize or avoid the formation of head-to-head dyads unfavourably affecting the presence of coplanar conformations of thiophene rings as a consequence of steric interactions between the side-chain substituents, both in solution and in the solid state. To this regard, non-symmetrically substituted monomers require therefore to perform the polymerization in the presence of highly demanding catalysts and reaction condition, whereas with symmetrically substituted oligothiophenic monomers containing the -substituents located far apart from the reacting sites, it is instead possible to obtain regioregular macromolecules by adopting more simple and economic polymerization methods, such as, e. g., the chemical oxidative polymerization with iron (III) trichloride. In order to verify how the polymer structure affects its optical activity, further poly-3-alkylthiophenes, substituted by an enantiomerically pure chiral alkyl group, namely poli[3,3”-di[2((S)-(+)-2-methylbutoxy)ethyl]-2,2’:5’,2”-terthiophene] (PDMBOETT), poli[3,3’di[2((S)-(+)-2-methylbutoxy)ethyl]-2,2’-bitiofene] (PDMBOEBT), poli[3,3””-didodecyl-4’,3”’-di(S)-(+)-2-methylbutyl-2,2’:5’,2”:5”,2”’:5”’,2””-quinquethiophene (PDDDMBQT) have been synthesized and characterized by instrumental techniques. The spectroscopic behaviour of thin films of poly(DDDMBQT) has been investigated in the solid state under different sample preparation procedures. It was also compared with the behaviour of polymers previously made. The experimental results are interpreted in terms of influence of the side-chain substituents on the extent of planarity of the polymeric chains and the formation of optically active chiral aggregates. In recent years conjugated block copolymers have received considerable attention. It is well known that conjugated block copolymers composed of two electronically different blocks can have morphologic and optical properties, that differ from those of their homopolymers. A recent study has also shown that the electronic properties and the supramolecular organization of one conjugated block can also be influenced by the other block. In order to study better this behavior, a new conjugated block copolymers, composed of a regioregular hydrophylic block and a regioregular hydrophobic block namely poli[3[2-(2-metossietossi)etossi]metiltiofene]-co- poli[3(1-octilossi)tiofene], has been synthesized and characterized.

Sistemi liquido cristallini complessi: simulazioni al calcolatore e studi ESR

The aim of this PhD thesis was to study at a microscopic level different liquid crystal (LC) systems, in order to determine their physical properties, resorting to two distinct methodologies, one involving computer simulations, and the other spectroscopic techniques, in particular electron spin resonance (ESR) spectroscopy. By means of the computer simulation approach we tried to demonstrate this tool effectiveness for calculating anisotropic static properties of a LC material, as well as for predicting its behaviour and features. This required the development and adoption of suitable molecular models based on a convenient intermolecular potentials reflecting the essential molecular features of the investigated system. In particular, concerning the simulation approach, we have set up models for discotic liquid crystal dimers and we have studied, by means of Monte Carlo simulations, their phase behaviour and self­-assembling properties, with respect to the simple monomer case. Each discotic dimer is described by two oblate Gay­Berne ellipsoids connected by a flexible spacer, modelled by a harmonic "spring" of three different lengths. In particular we investigated the effects of dimerization on the transition temperatures, as well as on the characteristics of molecular aggregation displayed and the relative orientational order. Moving to the experimental results, among the many experimental techniques that are typically employed to evaluate LC system distinctive features, ESR has proved to be a powerful tool in microscopic scale investigation of the properties, structure, order and dynamics of these materials. We have taken advantage of the high sensitivity of the ESR spin probe technique to investigate increasingly complex LC systems ranging from devices constituted by a polymer matrix in which LC molecules are confined in shape of nano- droplets, as well as biaxial liquid crystalline elastomers, and dimers whose monomeric units or lateral groups are constituted by rod-like mesogens (11BCB). Reflection-mode holographic-polymer dispersed liquid crystals (H-PDLCs) are devices in which LCs are confined into nanosized (50­-300 nm) droplets, arranged in layers which alternate with polymer layers, forming a diffraction grating. We have determined the configuration of the LC local director and we have derived a model of the nanodroplet organization inside the layers. Resorting also to additional information on the nanodroplet size and shape distribution provided by SEM images of the H-PDLC cross-section, the observed director configuration has been modeled as a bidimensional distribution of elongated nanodroplets whose long axis is, on the average, parallel to the layers and whose internal director configuration is a uniaxial quasi- monodomain aligned along the nanodroplet long axis. The results suggest that the molecular organization is dictated mainly by the confinement, explaining, at least in part, the need for switching voltages significantly higher and the observed faster turn-off times in H-PDLCs compared to standard PDLC devices. Liquid crystal elastomers consist in cross-linked polymers, in which mesogens represent the monomers constituting the main chain or the laterally attached side groups. They bring together three important aspects: orientational order in amorphous soft materials, responsive molecular shape and quenched topological constraints. In biaxial nematic liquid crystalline elastomers (BLCEs), two orthogonal directions, rather than the one of normal uniaxial nematic, can be controlled, greatly enhancing their potential value for applications as novel actuators. Two versions of a side-chain BLCEs were characterized: side­-on and end­-on. Many tests have been carried out on both types of LCE, the main features detected being the lack of a significant dynamical behaviour, together with a strong permanent alignment along the principal director, and the confirmation of the transition temperatures already determined by DSC measurements. The end­-on sample demonstrates a less hindered rotation of the side group mesogenic units and a greater freedom of alignment to the magnetic field, as already shown by previous NMR studies. Biaxial nematic ESR static spectra were also obtained on the basis of Molecular Dynamics generated biaxial configurations, to be compared to the experimentally determined ones, as a mean to establish a possible relation between biaxiality and the spectral features. This provides a concrete example of the advantages of combining the computer simulation and spectroscopic approaches. Finally, the dimer α,ω-bis(4'-cyanobiphenyl-4-yl)undecane (11BCB), synthesized in the "quest" for the biaxial nematic phase has been analysed. Its importance lies in the dimer significance as building blocks in the development of new materials to be employed in innovative technological applications, such as faster switching displays, resorting to the easier aligning ability of the secondary director in biaxial phases. A preliminary series of tests were performed revealing the population of mesogenic molecules as divided into two groups: one of elongated straightened conformers sharing a common director, and one of bent molecules, which display no order, being equally distributed in the three dimensions. Employing this model, the calculated values show a consistent trend, confirming at the same time the transition temperatures indicated by the DSC measurements, together with rotational diffusion tensor values that follow closely those of the constituting monomer 5CB.

Von zwei- zu dreidimensionalen Graphitausschnitten

Zusammenfassung: 'Von zwei- zu dreidimensionalen Graphitausschnitten'Dissertation Florian Dötz Die vorliegende Arbeit zeichnet den synthetischen Weg von zwei- zu dreidimensionalen Graphitausschnitten nach und thematisiert insbesondere die Schnittstelle dieser beiden Bereiche, die durch den Übergang von planaren Systemen zu räumlichen Strukturen verkörpert wird und daher die Darstellung nicht-planarer polycyclischer aromatischer Kohlenwasserstoffe (PAH) vorsieht. Diese Zielsetzung mündet in einer dreiteiligen Gliederung der angefertigten Dissertation und sieht im ersten Teil die Synthese planarer Graphitsegmente durch oxidative Cyclodehydrierung entsprechender Oligophenylvorläufer mit Eisen(III)chlorid vor, gefolgt von der Darstellung nicht-planarer PAHs mit denselben oxidativen Methoden sowie der Präparation und Charakterisierung dreidimensionaler, supramolekularer PAH-Aggregate.Der erste Abschnitt beschreibt die Synthese von kleineren PAHs als Modellverbindung für größere Systeme und ihre UV-spektroskopische Charakterisierung. Daran anknüpfend wird die Synthese mehrerer heteroatomsubstituierter Derivate des Hexa-peri-hexabenzocoronens (HBC) vorgestellt und ihre flüssigkristallinen Eigenschaften eingehend untersucht. Dabei wurde mit der oxidativen Cyclodehydrierung geeigneter Vorläufer auf Einkristalloberflächen ein neuer Weg zur Synthese dieser Verbindungen etabliert.Im Zentrum des zweiten Teils dieser Arbeit stand die Induktion von Nichtplanarität in ausgedehnten PAHs mit den im ersten Abschnitt entwickelten Synthesekonzepten. Hier konnte mit der erfolgreichen Darstellung eines 18fach methoxysubstituierten HBC-Derivats eine erstaunliche Krümmung des aromatischen Systems erreicht werden, wie durch Kristallstrukturanalyse gezeigt wurde. Anhand mehrerer Beispiele wurde ebenso die Leistungsfähigkeit der verwendeten Cyclodehydrierungsmethode verdeutlicht, da viele Vorläufermoleküle gegenüber den Reaktionsbedingungen nicht inert sind.Der letzte Teil dieser Arbeit beschreibt schließlich die Präparation und Charakterisierung dreidimensionaler, supramolekularer PAH-Aggregate auf der Basis von HBC-Amiden, deren Eigenschaften sich durch eine sorgfältige Wahl der jeweiligen Monomerbausteine manipulieren lassen. Bei Verwendung von chiralen Monomeren wird hier die Expression von supramolekularer Chiralität erreicht und durch spektroskopische und chiroptische Methoden belegt.

Synthese funktionalisierter Phenolpolymere durch HRP-katalysierte Polyrekombination

ZUSAMMENFASSUNG: Die durch das Enzym Horseradish Peroxidase katalysierte oxidative Polymerisation substituierter Phenole gewährt einen bequemen Zugang zu funktionalisierten Phenolpolymeren, deren Anwendung als Ersatz für konventionelle Phenol-Formaldehyd-Harze zur Zeit intensiv erforscht wird. Zur Zeit werden Polymerisation dieser Art in Mischungen aus organischen Lösungsmitteln (z.B. 1,4-Dioxan) und Puffer durchgeführt. Im Rahmen dieser Arbeit wurde eine HRP-katalysierte Phenolpolymerisation von wasserunlöslichen Methacryloyl- und Maleinimid-substituierten Phenolen in 100% Pufferlösung durch die Verwendung von 2,6-methylierten Cyclodextrinen als carrier erreicht. Die so hergestellten Oligomere wurden mit Styrol und MMA copolymerisiert. Weitere Untersuchungen hatten die Synthese photoreaktiver Phenolpolymere mit Zimtsäure- oder Nitrongruppen in der Seitenkette, die Synthese thermisch vernetzbarer Phenolcopolymere aus Furan-2-carboxylsäure-(4-hydroxy-phenyl)-amid und N-methacryloyl-11-aminoundecanoyl-4-hydroxyanilid sowie die Synthese eines Redoxpolymeren ausgehend von 4-Aminophenol zum Ziel. Daneben wurden Strategien zur enzymatisch katalysierten Synthese von Poly[para-phenylenen], hyperverzweigten Phenolpolymeren und biologisch aktiven Phenolpolymeren entwickelt, und detaillierte Untersuchungen zum Polymerisationsmechanismus und zur Struktur der entstehenden Phenolpolymere vorgestellt. Die vorgestellten Phenolpolymere bestehen hoechstwahrscheinlich aus polyaromatischen Helices, da diese p-substituierten Phenole während des Rekombinationsprozesses bevorzugt an den ortho-Positionen rekombinieren.

Liquid crystalline oligofluorenes and their derivatives

Homo-oligofluorenes (OFn), polyfluorenes (PF2/6) and oligofluorenes with one fluorenenone group in the center (OFnK) were synthesized. They were used as model compounds to understand of the structure-property relationships of polyfluorenes and the origin of the green emission in the photoluminescence (after photooxidation of the PFs) and the electroluminescence (EL) spectra. The electronic, electrochemical properties, thermal behavior, supramolecular self-assembly, and photophysical properties of OFn, PF2/6 and OFnK were investigated. Oligofluorenes with 2-ethylhexyl side chain (OF2-OF7) from the dimer up to the heptamer were prepared by a series of stepwise transition metal mediated Suzuki and Yamamoto coupling reactions. Polyfluorene was synthesized by Yamamoto coupling of 2,7-dibromo-9,9-bis(2-ethylhexyl)fluorene. Oligofluorenes with one fluorenone group in the center (OF3K, OF5K, OF7K) were prepared by Suzuki coupling between the monoboronic fluorenyl monomer, dimer, trimer and 2, 7-dibromofluorenone. The electrochemical and electronic properties of homo-oligofluorenes (OFn) were systematically studied by several combined techniques such as cyclic voltammetry, differential pulse voltammetry, UV-vis absorption spectroscopy, steady and time-resolved fluorescence spectroscopy. It was found that the oligofluorenes behave like classical conjugated oligomers, i.e., with the increase of the chain-length, the corresponding oxidation potential, the absorption and emission maximum, ionization potential, electron affinity, band gap and the photoluminescence lifetime displayed a very good linear relation with the reciprocal number of the fluorene units (1/n). The extrapolation of these linear relations to infinite chain length predicted the electrochemical and electronic properties of the corresponding polyfluorenes. The thermal behavior, single-crystal structure and supramolecular packing, alignment properties, and molecular dynamics of the homo-oligofluorenes (OFn) up to the polymer were studied using techniques such as TGA, DSC, WAXS, POM and DS. The OFn from tetramer to heptamer show a smectic liquid crystalline phase with clearly defined isotropization temperature. The oligomers do show a glass transition which exhibits n-1 dependence and allows extrapolation to a hypothetical glass transition of the polymer at around 64 °C. A smectic packing and helix-like conformation for the oligofluorenes from tetramer to heptamer was supported by WAXS experiments, simulation, and single-crystal structure of some oligofluorene derivatives. Oligofluorenes were aligned more easily than the corresponding polymer, and the alignability increased with the molecular length from tetramer to heptamer. The molecular dynamics in a series of oligofluorenes up to the polymer was studied using dielectric spectroscopy. The photophysical properties of OFn and PF2/6 were investigated by the steady-state spectra (UV-vis absorption and fluorescence spectra) and time-resolved fluorescence spectra both in solution and thin film. The time-resolved fluorescence spectra of the oligofluorenes were measured by streak camera and gate detection technique. The lifetime of the oligofluorenes decreased with the extension of the chain-length. No green emission was observed in CW, prompt and delayed fluorescence for oligofluorenes in m-THF and film at RT and 77K. Phosphorescence was observed for oligofluorenes in frozen dilute m-THF solution at 77K and its lifetime increased with length of oligofluorenes. A linear relation was obtained for triplet energy and singlet energy as a function of the reciprocal degree of polymerization, and the singlet-triplet energy gap (S1-T1) was found to decrease with the increase of degree of polymerization. Oligofluorenes with one fluorenone unit at the center were used as model compounds to understand the origin of the low-energy (“green”) emission band in the photoluminescence and electroluminescence spectra of polyfluorenes. Their electrochemical properties were investigated by CV, and the ionization potential (Ip) and electron affinity (Ea) were calculated from the onset of oxidation and reduction of OFnK. The photophysical properties of OFnK were studied in dilute solution and thin film by steady-state spectra and time-resolved fluorescence spectra. A strong green emission accompanied with a weak blue emission were obtained in solution and only green emission was observed on film. The strong green emission of OFnK suggested that rapid energy transfer takes place from higher energy sites (fluorene segments) to lower energy sites (fluorenone unit) prior to the radiative decay of the excited species. The fluorescence spectra of OFnK also showed solvatochromism. Monoexponential decay behaviour was observed by time-resolved fluorescence measurements. In addition, the site-selective excitation and concentration dependence of the fluorescence spectra were investigated. The ratio of green and blue emission band intensities increases with the increase of the concentration. The observed strong concentration dependence of the green emission band in solution suggests that increased interchain interactions among the fluorenone-containing oligofluorene chain enhanced the emission from the fluorenone defects at higher concentration. On the other hand, the mono-exponential decay behaviour and power dependence were not influenced significantly by the concentration. We have ruled out the possibility that the green emission band originates from aggregates or excimer formation. Energy transfer was further investigated using a model system of a polyfluorene doped by OFnK. Förster-type energy transfer took place from PF2/6 to OFnK, and the energy transfer efficiency increased with increasing of the concentration of OFnK. Efficient funneling of excitation energy from the high-energy fluorene segments to the low-energy fluorenone defects results from energy migration by hopping of excitations along a single polymer chain until they are trapped on the fluorenone defects on that chain or transferred onto neighbouring chains by Förster-type interchain energy transfer process. These results imply that the red-shifted emission in polyfluorenes can originate from (usually undesirable) keto groups at the bridging carbon atoms-especially if the samples have been subject to photo- or electro-oxidation or if fluorenone units are present due to an improper purification of the monomers prior to polymerization.

Cellulose based Lithium ion polymer electrolytes for Lithium batteries

The separator membrane in batteries and fuel cells is of crucial importance for the function of these devices. In lithium ion batteries the separator membrane as well as the polymer matrix of the electrodes consists of polymer electrolytes which are lithium ion conductors. To overcome the disadvantage of currently used polymer electrolytes which are highly swollen with liquids and thus mechanically and electrochemically unstable, the goal of this work is a new generation of solid polymer electrolytes with a rigid backbone and a soft side chain structure. Moreover the novel material should be based on cheap substrates and its synthesis should not be complicated aiming at low overall costs. The new materials are based on hydroxypropylcellulose and oligoethyleneoxide derivatives as starting materials. The grafting of the oligoethyleneoxide side chains onto the cellulose was carried out following two synthetic methods. One is based on a bromide derivative and another based on p-toluolsulfonyl as a leaving group. The side chain reagents were prepared form tri(ethylene glycol) monoethyl ether. In order to improve the mechanical properties the materials were crosslinked. Two different conceptions have been engaged based on either urethane chemistry or photosensitive dimethyl-maleinimide derivatives. PEO - graft - cellulose derivatives with a high degree of substitution between 2,9 and 3,0 were blended with lithium trifluoromethane-sulfonate, lithium bis(trifluorosulfone)imide and lithium tetrafluoroborate. The molar ratios were in the range from 0,02 to 0,2 [Li]/[O]. The products have been characterized with nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and laserlight scattering (LS) with respect to their degree of substitution and molecular weight. The effect of salt concentration on ionic conductivity, thermal behaviour and morphology has been investiga-ted with impedance spectroscopy, differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The crosslinking reactions were controlled with dynamic mechanical analysis (DMS). The degree of substitution of our products is varying between 2,8 and 3,0 as determined by NMR. PEO - graft - cellulose derivatives are highly viscous liquids at room temperature with glass transition temperatures around 215 K. The glass transition temperature for the Lithium salt complexes of PEO - graft - cellulose deri-vatives increase with increasing salt content. The maximum conductivity at room temperature is about 10-4 and at 100°C around 10-3 Scm-1. The presence of lithium salt decreases the thermal stability of the complexes in comparison to pure PEO - graft - cellulose derivatives. Complexes heated over 140 – 150°C completely lose their ionic conductivity. The temperature dependence of the conductivity presented as Arrhenius-type plots for all samples is similar in shape and follows a VTF behaviour. This proofs that the ionic transport is closely related to the segmental motions of the polymer chains. Novel cellulose derivatives with grafted oligoethylen-oxide side chains with well-defined chemical structure and high side chain grafting density have been synthesized. Cellulose was chosen as stiff, rod like macromolecule for the backbone while oligoethylen-oxides are chosen as flexible side chains. A maximum grafting density of 3.0 have been obtained. The best conductivity reaches 10-3 Scm-1 at 100°C for a Li-triflate salt complex with a [Li]/[O] ratio of 0.8. The cross-linked complexes containing the lithium salts form elastomeric films with convenient mechanical stability. Our method of cellulose modification is based on relatively cheap and commercially available substrates and as such appears to be a promising alternative for industrial applications.

Wasserfreie Protonenleiter für Brennstoffzellen auf der Basis von Imidazol und Benzimidazol

Mit Hilfe von Brennstoffzellen wird eine effiziente Energieumwandlung von chemischer in elektrische Energie möglich. Die kommerziellen PEM-Brennstoffzellen benutzen Membra-nen, die zum Erreichen hoher Leitfähigkeiten eine wässrige Phase erfordern, in der der Proto-nentransport stattfindet. Somit wird die Betriebstemperatur durch den Siedepunkt des Wassers limitiert. Die verwendeten Pt-Katalysatoren zeigen bei niedrigen Temperaturen eine höhere Empfindlichkeit gegenüber CO, dass im Reformierungsprozess bei der Erzeugung von Was-serstoff entsteht. Austausch der wässrigen Phase gegen Heterozyklen, die ein zu Wasser ver-gleichbares Wasserstoffbrückennetzwerk aufbauen, in dem der Protonentransport stattfinden kann, ermöglicht eine höhere Betriebstemperatur. Durch das im Laufe des Brennstoffzellen-betriebs gebildete Wasser, können die Heterozyklen verdünnt bzw. komplett aus der Memb-ran ausgewaschen werden. Daher ist es erforderlich, die Ladungsträger an ein Polymerrück-grat zu binden, so dass sie eine hohe Beweglichkeit und Konzentration, die denen in der flüs-sigen Phase einer konventionellen Membran entsprechen, aufweisen. Diese Arbeit beschreibt die Synthese und Charakterisierung von Protonenleitern, die ohne eine flüssige Phase auskommen, da sie bereits protonische Leitfähigkeit als intrinsische Ei-genschaft zeigen. Es wurden verschiedene imidazol- bzw. benzimidazolhaltige Dimere und Polythiophene, in denen Benzimidazol in der Seitenkette über verschieden flexible Spacer mit dem Polymerrückgrat verbunden ist, synthetisiert. Die Materialien wurden in undotierten Zu-stand und nach Dotierung mit geringen Mengen Phosphorsäure umfassend charakterisiert und auf thermisches Verhalten, Stabilität und Leitfähigkeit untersucht. Die benzimidazolhaltigen Dimere weisen mit 250 °C die höchsten Zersetzungstemperaturen auf. Mit zunehmender Temperatur kann in allen Fällen eine Erhöhung der Leitfähigkeit beobachtet werden, die sich in der Arrhenius-Auftragung durch eine Gerade anpassen lässt, somit kann der Protonentrans-port durch einen Protonen-hüpfmechanismus beschrieben werden. Die höchste beobachtete Leitfähigkeit liegt im Bereich von 10-6 S/cm bei 160 °C. Durch Zusatz von Phosphorsäure kann die Leitfähigkeit z.T. um einige Größenordnungen gesteigert werden. Eine Ausnahme bilden die Polythiophene, die sowohl protonische als auch elektronische Leitfähigkeit besit-zen. Hier führt die Säure zu einer Lokalisierung der Ladungsträger, so dass die elektronische Leitfähigkeit eingeschränkt wird.

Benzothiazoliumsalze als Photoinitiatoren für kationische Epoxidpolymerisationen

In dieser Arbeit wurden neuartige substituierte N-Benzylbenzothiazoliumhexa-fluorophosphate und –antimonate synthetisiert und hinsichtlich ihre Wirksamkeit als photo- und thermolatente Initiatoren für Epoxidpolymerisationen untersucht. Zur Synthese der Benzothiazoliumderivate wurden zunächst substituierte Benzothiazole nach verschiedenen Verfahren hergestellt, diese mit den entsprechenden Benzylbromiden quaternisiert und die N-quaternären Bromide zu den Hexafluorophosphaten bzw. –antimonaten umgesalzt. Neben den niedermolekularen Benzothiazoliumsalzen wurden auch Copolymere mit dieser Struktur in der Seitenkette durch radikalische Copolymerisation vinylsubstituierter N-quaternärer Benzothiazoliumsalze mit MMA hergestellt. Sowohl die niedermolekularen als auch die polymergebundenen Benzothiazoliumhexafluorophosphate erwiesen sich als effektive direkte kationische Photo- und Thermoinitiatoren für die Polymerisation von Epoxiden. Durch die Einführung auxochromer Ethergruppierungen konnte eine bathochrome Verschiebung der UV-Absorptionswellenlänge des energieärmsten elektronischen Überganges erreicht werden. Kinetische IR-Studien der kationischen Polymerisation von Glycidylphenylether (GPE) im Nassfilm unter Bestrahlung in Gegenwart der hergestellten Benzothiazoliumsalze als Photoinitiatoren zeigten dass durch die so erreichte verbesserte Ausnutzung der einwirkenden Strahlung die kationische Photoinitiatoreffektivität deutlich gesteigert werden konnte. Der Zusatz eines photolytischen Radikalbildners führte zu einer weiteren Steigerung der Photopolymerisationsgeschwindigkeit und zu einer Umkehr der beobacheteten Initiatoreffektivitäten. UV-, 1H NMR-, sowie MALDI-TOF- Untersuchungen, sowie die vollständige Unterdrückung der Photopolymerisation durch den Protonenfänger DBP deuten auf die photolytische Generierung von Protonen als initiierende Spezies der photokationischen Polymerisation und DSC- und 1H-NMR Ergebnisse auf die thermische Generierung von Benzylkationen als initiierende Spezies der thermischen Polymerisation hin.

Visualization, manipulation and force spectroscopy of cylindrical polymer brushes

The Ph.D. thesis deals with the conformational study of individual cylindrical polymer brush molecules using atomic force microscopy (AFM). Imaging combined with single molecule manipulation has been used to unravel questions concerning conformational changes, desorption behavior and mechanical properties of individual macromolecules and supramolecular structures. In the first part of the thesis (chapter 5) molecular conformations of cylindrical polymer brushes with poly-(N-isopropylacrylamide) (PNIPAM) side chains were studied in various environmental conditions. Also micelle formation of cylindrical brush-coil blockcopolymers with polyacrylic acid side chains and polystyrene coil have been visualized. In chapter 6 the mechanical properties of single cylindrical polymer brushes with (PNIPAM) side chains were investigated. Assuming that the brushes adopt equilibrium conformation on the surface, an average persistence length of lp= (29 ± 3) nm was determined by the end-to-end distance vs. contour length analysis in terms of the wormlike chain (WLC) model. Stretching experiments suggest that an exact determination of the persistence length using force extension curves is impeded by the contribution of the side chains. Modeling the stretching of the bottle brush molecule as extension of a dual spring (side chain and main chain) explains the frequently observed very low persistence length arising from a dominant contribution of the side chain elasticity at small overall contour lengths. It has been shown that it is possible to estimate the “true” persistence length of the bottle brush molecule from the intercept of a linear extrapolation of the inverse square root of the apparent persistence length vs. the inverse contour length plot. By virtue of this procedure a “true” persistence length of 140 nm for the PNIPAM brush molecules is predicted. Chapter 7 and 8 deal with the force-extension behavior of PNIPAM cylindrical brushes studied in poor solvent conditions. The behavior is shown to be qualitatively different from that in a good solvent. Force induced globule-cylinder conformational changes are monitored using “molecule specific force spectroscopy” which is a combined AFM imaging and SMFS technique. An interesting behavior of the unfolding-folding transitions of single collapsed PNIPAM brush molecules has been observed by force spectroscopy using the so called “fly-fishing” mode. A plateau force is observed upon unfolding the collapsed molecule, which is attributed to a phase transition from a collapsed brush to a stretched conformation. Chapter 9 describes the desorption behavior of single cylindrical polyelectrolyte brushes with poly-L-lysine side chains deposited on a mica surface using the “molecule specific force spectroscopy” technique to resolve statistical discrepancies usually observed in SMFS experiments. Imaging of the brushes and inferring the persistence length from a end-to-end distance vs. contour length analysis results in an average persistence length of lp = (25 ± 5) nm assuming that the chains adopt their equilibrium conformation on the surface. Stretching experiments carried out on individual poly-L-lysine brush molecules by force spectroscopy using the “fly-fishing” mode provide a persistence length in the range of 7-23 nm in reasonable accordance with the imaging results. In chapter 10 the conformational behavior of cylindrical poly-L-lysine brush-sodium dodecyl sulfate complexes was studied using AFM imaging. Surfactant induced cylinder to helix like to globule conformational transitions were observed.

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.

Synthesis and characterization of polyelectrolyte brushes

On the pathway to synthesizing synthetic model systems for human cartilage, macroinitiators for the ATRP of styrene sulfonate esters with different chain lengths and initiation site densities from 10 % to 100 % were synthesized. Polymer brushes from styrene sulfonate ethyl ester and styrene sulfonate dodecyl ester with varying grafting density, backbone length and side chain length were synthesized and characterized by 1H-NMR, AUC, AFM, TEM, and in the case of the ethyl esters, GPC-MALLS. Polyelectrolyte brushes from styrene sulfonate were synthesized from the corresponding esters. These brushes were characterized in solution (GPC-MALLS, static and dynamic light scattering, SANS, 1H-NMR) and on solid interfaces (AFM and TEM). It was shown that these brushes may form extended aggregates in solution. The aggregation behavior and the size and shape of the aggregates depend on the side chain length and the degree of saponification. For samples with identical backbone and side chain length, but varying degrees of ester hydrolysis, marked differences in the aggregation behavior were observed. A functionalized ATRP macroinitiator with a positively charged head group was synthesized and employed for the synthesis of a functionalized polyelectrolyte brush. These brushes were found to form complexes with negatively charged latex particles and are thus suitable as proteoglycan models in the proteoglycan-hyaluronic acid complex.

Interpolyelektrolytkomplexe zylindrischer Bürstenpolymere

Die elektrostatische Wechselwirkung zwischen entgegengesetzt geladenen Polyelektrolyten führt zur spontanen Bildung von Interpolyelektrolytkomplexen. Besonders im Fokus des akademischen und biotechnologischen Interesses stehen derzeit Komplexe aus DNA und synthetischen Polykationen, da eine Anwendung dieser speziellen Interpolyelektrolytkomplexe in der nicht-viralen Gentherapie vielfältig diskutiert wird. Ziel der vorliegenden Arbeit war es, den Einfluss von Kettensteifheit auf die Bildung von Interpolyelektrolytkomplexen zu untersuchen und dabei Wege aufzuzeigen, die eine Kontrolle der Topologie von Interpolyelektrolytkomplexen ermöglichen. Neben dem topologischen Einfluss wurde untersucht, wie durch Komplexierung hochmolekularer Polyelektrolyte equilibrierbare Strukturen erhalten werden können. Als Modellsystem für diese Untersuchungen wurden zylindrische Bürstenpolymere verwendet, denen als topologischer „Kontrast“ das Komplexierungsverhalten kommerzieller PAMAM-G5-Dendrimere mit kugelförmiger Topologie gegenüber gestellt wurde. Um den Ladungsgrad des Bürstenpolymers beliebig variieren zu können, wurden Bürstenpolymere mit Poly(ethylenimin)-Seitenketten synthetisiert, deren Ladungsdichte über den Protonierungsgrad einstellbar ist. Die vorliegende Arbeit zeigt, wie diese mit Hilfe der Makromonomermethode hergestellt werden konnten. Die Komplexbildung von DNA mit semiflexiblen zylindrischen Bürstenpolymeren mit unterschiedlichen Seitenketten und Ladungsdichten in wässriger Lösung hat gezeigt, dass diese in allen untersuchten Fällen unter kinetischer Kontrolle verläuft und Nicht-Gleichgewichtsstrukturen gebildet werden. Sehr überraschend wurde festgestellt, dass die Größen der mit vorgelegter DNA gebildeten Komplexe ungeachtet des verwendeten Polykations identisch sind und DNA-Komplexe mit einem Radius von 30 bis 50 nm und einer kugelförmigen Topologie resultieren. Diese kinetisch kontrollierte Komplexbildung konnte in nicht-wässriger Lösung durch starke Reduktion der Anzahl wechselwirkender Ladungen verhindert werden, so dass eine thermodynamische Kontrolle möglich wurde. Unter diesen Bedingungen ist es gelungen, aus hochgeladenen Poly(styrolsulfonat)-Bürsten mit modifizierten Poly(ethylenimin)-Bürsten oder PAMAM-Dendrimeren Komplexe zylindrischer Topologie herzu-stellen. Für letztere konnte darüber hinaus postuliert werden, dass diese Komplexe eine dichteste Packung der PAMAM-Dendrimere darstellen, für deren Bildung das Polyanion mit seiner größeren Konturlänge und seiner zylindrischen Topologie als Templat dient.

Untersuchung der DNA-bindenden Eigenschaften neuer Nukleobasen-gekoppelter Pyrrolcarboxamide, Combilexine und Hetaren[a]carbazol-Derivate: Validierung und Etablierung von in-vitro- und in-silico-Methoden

Da maligne Neoplasien durch Mutationen in Proto-Onko- und/oder Tumorsuppressorgenen ausgelöst werden, stellt die DNA eines der wichtigsten Targets für die Entwicklung neuer Zytostatika dar. Auch bei den im Arbeitskreis Pindur designten und synthetisier-ten Verbindungen der Nukleobasen-gekoppelten Pyrrolcarboxamid-, der Hetaren[a]carbazol- und der Combilexin-Reihe handelt es sich um DNA-Liganden mit potentiell antitumoraktiven Eigenschaf-ten. Die einen dualen Bindemodus aufweisenden Combilexine bestehen aus einem Interkalator (u. a. Naphthalimid, Acridon), der über einen Linker variabler Kettenlänge mit einer rinnenbin-denden, von Netropsin abgeleiteten Bispyrrol-, oder einer bioisosteren Imidazol-, Thiazol- oder Thiophen-pyrrolcarboxamid-struktur verknüpft ist. Das N-terminale Ende der Combilexine wird von einer N,N-Dimethylaminopropyl- oder -ethyl-Seitenkette gebildet. Die DNA-Affinitäten der Liganden wurden mittels Tm-Wert-Messung-en bestimmt. Diese Denaturierungsexperimente wurden sowohl mit poly(dAdT)2- als auch mit Thymus-DNA (~42% GC-Anteil) durchge-führt, um Aussagen zur Stärke und zur Sequenzselektivität der DNA-Bindung machen zu können. Des Weiteren wurden die Bindekon-stanten einiger ausgewählter Vertreter mit Hilfe des Ethidium-bromid-Verdrängungsassays ermittelt; einige Testverbindungen wurden zudem auf potentiell vorhandene, TOPO I-inhibierende Eigenschaften untersucht. Diese biochemischen und biophysika-lischen Tests wurden durch Molecular Modelling-Studien ergänzt, die die Berechnung von molekularen Eigenschaften, die Durch-führung von Konformerenanalysen und die Simulation von DNA-Ligand-Komplexen (Docking) umfassten. Durch Korrelation der in vitro-Befunde mit den in silico-Daten gelang es, vor allem für die Substanzklasse der Combilexine einige richtungweisende Struktur-Wirkungsbeziehungen aufzustellen. So konnte gezeigt werden, dass die Einführung eines Imidazol-Rings in die rinnen-bindende Hetaren-pyrrolcarboxamid-Struktur der Combilexine aufgrund der H-Brücken-Akzeptor-Funktion des sp2-hybridisierten N-Atoms eine Verschiebung der Sequenzselektivität der DNA-Bindung von AT- zu GC-reichen Arealen der DNA bedingt. Zudem erwies sich ein C3-Linker für die Verknüpfung des Naphthalimids mit dem rinnenbindenden Strukturelement als am besten geeignet, während bei den Acridon-Derivaten die Verbindungen mit einem N-terminalen Buttersäure-Linker die höchste DNA-Affinität aufwiesen. Dies ist sehr wahrscheinlich auf die im Vergleich zum Naphthalimid-Molekül geringere y-Achsen-Ausdehnung (bzgl. eines x/y-Koordinatensystems) des Acridons zurückzuführen. Die ermittelten Struktur-Wirkungsbeziehungen können dazu herangezogen werden, das rationale Design neuer DNA-Liganden mit potentiell stärkerer DNA-Bindung zu optimieren.