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Immunity, Inflammation and Cancer: The role of Foxp3, TLR7 and TLR8 in gastrointestinal cancer
(2015)
Regulatory T cells (Treg) expressing the transcription factor forkhead box protein P3 (Foxp3) have been demonstrated to mediate evasion from anti-tumor immune responses during tumor progression. Moreover, Foxp3 expression by tumor cells themselves may allow them to counteract effector T cell responses, resulting in a survival benefit of the tumor. For gastrointestinal cancers, in particular pancreatic and colorectal cancer (CRC), the clinical relevance of Foxp3 is not clear to date. Therefore the aim of this study was to analyze its impact in CRC and pancreatic cancer. To determine the relevance of Foxp3 for tumor progression and patient survival, gene and protein analysis of human pancreatic and colon cancer cell lines as well as tumor tissues from patients with CRC was performed. The results derived from the patients with CRC were correlated with clinicopathological parameters and patients’ overall survival. Cancer cell mediated Foxp3 expression in vitro was demonstrated in human pancreatic cancer cell lines PANC1, PaCa DD 135, PaCa DD 159 and PaCa DD 185 as well as in human colon cancer cell lines SW480 and SW620. Additionally, Foxp3 expressing cancer cells were found in ex vivo tumor tissue samples of patients with CRC. The percentage of Foxp3+ cancer cells increased from stages UICC I/II to UICC III/IV compared to normal tissue. Moreover, high tumor cell mediated Foxp3 expression was associated with poor prognosis compared to patients with low Foxp3 expression. In contrast, low and high Foxp3 level in tumor infiltrating Treg cells demonstrated no significant differences in patients’ overall survival. Correlation analysis demonstrated a significant association of Foxp3 cancer cell expression with the expression of immunosuppressive cytokines IL-10 and TGF-β. These findings suggest that Immunosuppressive cytokines such as IL-10 and TGF-β released by rather Foxp3+ cancer cells than Foxp3+ Treg cells may inhibit the activation of naive T cells, hence limiting antitumor immune responses and favoring tumorigenesis and progression.
Chronic inflammation has been shown to be an important epigenetic and environmental factor in numerous tumor entities. Recent data suggest that tumorigenesis and tumor progression may be associated with inflammation-triggered activation of Toll-like receptors (TLR). In this study, the specific impact of both TLR7 and TLR8 expression and signaling on tumor cell proliferation and chemoresistance is analyzed in inflammation linked CRC and pancreatic cancer. By gene and protein expression analysis of human pancreatic and colon cancer cell lines TLR7 and TLR8 expression was determined in vitro. Additionally, expression of TLR7/TLR8 in UICC stage I-IV pancreatic cancer, chronic pancreatitis and normal pancreatic tissue was examined. For in vitro/in vivo studies TLR7/TLR8 overexpressing PANC1 cell lines were generated and analyzed for effects of TLR expression and stimulation on tumor cell proliferation and chemoresistance. Cancer cell mediated TLR7 and TLR8 expression in vitro was demonstrated in human colon cancer cell lines SW480, SW620 and HT-29 as well as in primary pancreatic cancer cell lines PaCa DD 135, PaCa DD 159 and PaCa DD 185. Additionally, TLR7 and TLR8 expressing tumor cells were found in ex vivo tissue samples of patients with pancreatic cancer and chronic pancreatitis. Significantly elevated expression levels of TLR7 and TLR8 were found in advanced tumor stages (UICC III) compared to early tumor stages (UICC II) and chronic pancreatitis. No or occasionally low expression was detected in normal pancreatic tissue. In contrast to the tissues from patients with pancreatic cancer or chronic pancreatitis, established pancreatic tumor cell lines express only very low levels of TLR7 and TLR8. Therefore, for in vitro and xenograft studies TLR7 or TLR8 overexpressing PANC1 cells were generated. Proliferation promoting effects of TLR7 and TLR8 expression and stimulation with R848 were detected in vitro. Additionally, increased tumor growth of TLR expressing PANC1 cells was demonstrated in subcutaneously injected Balb/c nude mice. Interestingly, activation of TLR7 or TLR8 induced not only an increase in tumor cell proliferation but also a strong chemoresistance of PANC1 cells against 5-fluorouracil (5-FU). Moreover, treatment with R848 resulted in elevated expression levels of NF-κB, COX-2 and inflammatory cytokines IL-1β, IL-8 and TNF-α, suggesting TLR7/8 signaling to contribute to an inflammatory, anti-apoptotic and proliferation promoting tumor microenvironment. These findings emphasize the particular role of TLR7 and TLR8 in inflammation related cancers and their relevance as potential targets for cancer therapy.
In this thesis the syntheses and detailed investigations on two foldable PBI systems were presented. The reversible, solvent-dependet folding/unfolding-behavior was used to study the ground and excited states properties of folda-dimer and folda-trimer by means of different spectroscopic methods as well as theoretical studies. The switching between charge transfer or excimer formation pathways of photoexcited molecules influenced by the spatial arrangement of chromophores within defined dye systems illustrates the impact of conformational preferences on functional properties.
This thesis focuses on the investigation of the electronic structure of amino acids and
salts in aqueous solution using X-ray spectroscopic methods. Both material groups are
of fundamental importance with regards to many physiological reactions, especially
for the Hofmeister effect which describes the solubility of proteins in salt solutions.
Hence, the investigation of the electronic structure of amino acids and the influence of
ions on the hydrogen bonding network of liquid water are important milestones to a
deeper understanding of the Hofmeister series.
Besides investigating the electronic structure of amino acids in aqueous solution,
the spectra were used to develop a building block model of the spectral fingerprints of
the functional groups and were compared to spectral signatures of suitable reference
molecules. In the framework of this thesis, it is shown that the building block approach
is a useful tool with allows the interpretation of spectral signatures of considerably
more complex molecules
In this work, the focus lies on the investigation of the occupied and unoccupied
electronic states of molecules in solid state, as well as in aqueous solution. Hereby,
different X-ray spectroscopic methods were applied. X-ray emission spectroscopy
(XES) was used to probe the occupied electronic structure of the solution, while the
unoccupied electronic structure was addressed by using X-ray absorption spectroscopy
(XAS). Finally, resonant inelastic X-ray scattering (RIXS) as a combination of XAS
and XES measurements provides the combined information about the unoccupied and
occupied molecular levels. The element specific character of the three measurement
methods is a feature which allows the investigation of the local electronic structure of
a single functional group. With RIXS, also non-equivalent atoms of the same element
can be addressed separately.
Within this thesis firstly, a library of the XE spectra of all 20 proteinogenic amino
acids in zwitterionic form is presented. From this sample-set XES fingerprints of
the protonated alpha-amino group NH3+ and the deprotonated carboxylic group COO- were evaluated and used to identify the XES fingerprints of the nitrogen and oxygen
containing functional groups of the side chains of the amino acids. The data is discussed
based on a building block approach. Furthermore, the XE spectra of the functional
groups of lysine and histidine, namely the NH2 group and the C3N2H4 ring structure,
are both compared to XE spectra of suitable reference molecules (imidazole, ammonia
and methylamine). It is found that the XE and RIXS spectra of the side chains of lysine
and histidine show large similarities to the XE spectra of the reference molecules. This
agreement in the XE and RIXS spectra allows a qualitative investigation of XE and
RIXS spectra of more complex amino acids using the XE and RIXS spectra of suitable
reference molecules.
The chemical structure of histidine and proline is quite different from the structures
of the other proteinogenic amino acids. Due to the unique chemical structure of
the side chain which in both cases consists of a heterocyclic ring structure, these two
amino acids were investigated in more detail. Zubavichus et al. [1] have shown that
amino acids are decomposing while exposed to X-ray radiation of the experiment. The
damage is irreversible and molecular fragments can adsorb on the membrane of the
experimental setup. This contamination can also create a spectral signature which
then overlaps with the signal of the solution and which complicates the interpretation
of the data. To record spectra which are free from contributions of adsorbed molecular
fragments on the membrane, the adsorption behavior was investigated.
In contrast to the solid phase in which the amino acids are present as salts in one
electronic conformation, the charge state of the amino acids can be manipulated in
aqueous solution by tuning the pH-value. By doing this, all possible charge states are
accessible (cation, anion, zwitterion). In this work it is shown that also the spectra
of the different charge states can be modeled by the spectra of suitable reference
molecules using the building block approach. The spectral changes occurring upon
protonation and deprotonation of the functional groups are explored and verified by
comparing them to theoretical calculations.
The comparison with measurements of pyrrolidine show that the electronic structure
which surrounds the nitrogen atom of proline is strongly influenced by the
ring structure of the side chain. Furthermore, the proline, pyrrolidine, and histidine
molecules are also degrading during the liquid sample measurements. This can be
observed by the detection of a new spectral component which increases with the
measurement time originating from the window membrane. In all cases, the speed of
the agglomeration of molecular fragments at the membrane was observed to be highly
sensitive to the pH value of the solution.
To understand the Hofmeister series, also the impact of the salt ions have to be
investigated. In this study the influence of potassium chloride (KCl) on the hydrogen
bond network of water was studied by using non-resonantly excited XES as well as
RIXS. A decreased dissociation of hydrogen molecules and changes in the molecular
vibrations could be detected. These changes were interpreted with a molecular
reorganization of the water molecules and a decreased number of hydrogen bonds.
This work sheds light on different aspects of the silicon vacancy in SiC:
(1) Defect creation via irradiation is shown both with electrons and neutrons. Optical properties have been determined: the excitation of the vacancy is most efficient at excitation wavelengths between 720nm and 800nm. The PL decay yields a characteristic excited state lifetime of (6.3±0.6)ns.
(2) Defect engineering, meaning the controlled creation of vacancies in SiC with varying neutron fluence. The defect density could be engineered over eight orders of magnitude. On the one hand, in the sample with highest emitter density, the huge PL signal could even be enhanced by factor of five via annealing mechanisms. On the other hand, in the low defect density samples, single defects with photostable room temperature NIR emission were doubtlessly proven. Their lifetime of around 7ns confirmed the value of the transient measurement.
(3) Also electrical excitation of the defects has been demonstrated in a SiC LED structure.
(4) The investigations revealed for the first time that silicon vacancies can even exist SiC nanocrystals down to sizes of about 60 nm. The defects in the nanocrystals show stable PL emission in the NIR and even magnetic resonance in the 600nm fraction.
In conclusion, this work ascertains on the one hand basic properties of the silicon vacancy in silicon carbide. On the other hand, proof-of-principle measurements test the potential for various defect-based applications of the vacancy in SiC, and confirm the feasibility of e.g. electrically driven single photon sources or nanosensing applications in the near future.
The goal of this thesis is to investigate conformal mappings onto circular arc polygon domains, i.e. domains that are bounded by polygons consisting of circular arcs instead of line segments.
Conformal mappings onto circular arc polygon domains contain parameters in addition to the classical parameters of the Schwarz-Christoffel transformation. To contribute to the parameter problem of conformal mappings from the unit disk onto circular arc polygon domains, we investigate two special cases of these mappings. In the first case we can describe the additional parameters if the bounding circular arc polygon is a polygon with straight sides. In the second case we provide an approximation for the additional parameters if the circular arc polygon domain satisfies some symmetry conditions. These results allow us to draw conclusions on the connection between these additional parameters and the classical parameters of the mapping.
For conformal mappings onto multiply connected circular arc polygon domains, we provide an alternative construction of the mapping formula without using the Schottky-Klein prime function. In the process of constructing our main result, mappings for domains of connectivity three or greater, we also provide a formula for conformal mappings onto doubly connected circular arc polygon domains. The comparison of these mapping formulas with already known mappings allows us to provide values for some of the parameters of the mappings onto doubly connected circular arc polygon domains if the image domain is a polygonal domain.
The different components of the mapping formula are constructed by using a slightly modified variant of the Poincaré theta series. This construction includes the design of a function to remove unwanted poles and of different versions of functions that are analytic on the domain of definition of the mapping functions and satisfy some special functional equations.
We also provide the necessary concepts to numerically evaluate the conformal mappings onto multiply connected circular arc polygon domains. As the evaluation of such a map requires the solution of a differential equation, we provide a possible configuration of curves inside the preimage domain to solve the equation along them in addition to a description of the procedure for computing either the formula for the doubly connected case or the case of connectivity three or greater. We also describe the procedures for solving the parameter problem for multiply connected circular arc polygon domains.
The oncogenic MYC protein is a transcriptional regulator of multiple cellular processes and is aberrantly activated in a wide range of human cancers. MYC is an unstable protein rapidly degraded by the ubiquitin-proteasome system. Ubiquitination can both positively and negatively affect MYC function, but its direct contribution to MYC-mediated transactivation remained unresolved.
To investigate how ubiquitination regulates MYC activity, a non-ubiquitinatable MYC mutant was characterized, in which all lysines are replaced by arginines (K-less MYC). The absence of ubiquitin-acceptor sites in K-less MYC resulted in a more stable protein, but did not affect cellular localization, chromatin-association or the ability to interact with known MYC interaction partners.
Unlike the wild type protein, K-less MYC was unable to promote proliferation in immortalized mammary epithelial cells. RNA- and ChIP-Sequencing analyses revealed that, although K-less MYC was present at MYC-regulated promoters, it was a weaker transcriptional regulator. The use of K-less MYC, a proteasomal inhibitor and reconstitution of individual lysine residues showed that proteasomal turnover of MYC is required for MYC target gene induction. ChIP-Sequencing of RNA polymerase II (RNAPII) revealed that MYC ubiquitination is dispensable for RNAPII recruitment and transcriptional initiation but is specifically required to promote transcriptional elongation. Turnover of MYC is required to stimulate histone acetylation at MYC-regulated promoters, which depends on a highly conserved region in MYC (MYC box II), thereby enabling the recruitment of BRD4 and P-TEFb and the release of elongating RNAPII from target promoters. Inhibition of MYC turnover enabled the identification of an intermediate in MYC-mediated transactivation, the association of MYC with the PAF complex, a positive elongation factor, suggesting that MYC acts as an assembly factor transferring elongation factors onto RNAPII. The interaction between MYC and the PAF complex occurs via a second highly conserved region in MYC’s amino terminus, MYC box I.
Collectively, the data of this work show that turnover of MYC coordinates histone acetylation with recruitment and transfer of elongation factors on RNAPII involving the cooperation of MYC box I and MYC box II.
Purpose – The purpose of this dissertation is to reveal the status quo of development of the grocery retailers’ internationalization process in China as well as to model future trends, opportunities and challenges within a very competitive market. Using several, geographically distant cities as case studies, this paper focuses on the development and outlook of different store formats, along with the development of competition in this respect by explicitly treating China not as a single market. The study thereby analyses historical and geographical diffusion in regard to store formats. The impacts of the main factors of change are discussed.
Design/methodology/approach – The dissertation reviews extensively the literature of grocery retail internationalization with special focus on China. In addition, it draws on primary research in the form of a wide range of expert interviews. As China´s ‘supermarket revolution’ is underway, an understanding of the local and foreign competition and the development of different store formats within different regions of China as well as their prospects, will be crucial to companies expanding into this area.
Findings – The study explains how grocery retailers have already entered the Chinese market with different store formats and how competition has and will further develop. In addition, the study reveals challenges and obstacles in regard to future market strategies, especially in regard to store formats and geographical regions.
Research limitations/implications – The study reveals the current landscape of the Chinese grocery retailing market and emphasizes important strategic pillars, modelling future implications and challenges for food retailers operating in China. Because China is a vast country this dissertation forms only a small part of the geographical evolution process in regard to store formats and competition.
Practical implications – Explores current understanding of the internationalization process in China by considering different format choices. Supplementary, the dissertation proposes an outlook of competition enlargement, prospects of format development and therewith strategic implications within different regions as well as a future research agenda.
Originality / value – Contributes to the understanding of the Chinese grocery retailing market. Furthermore, it is among the first to critically explore possible future developments in regard to store formats and competition within a geographical context in China
In summary, we have prepared single-wall carbon nanotube (SWNT) thin films by the method of evaporation-induced self-assembly (EISA). Using the scalable two-plate or lens setups, sorts of different film types or patterns of SWNTs has been successfully fabricated directly from the evaporation of solvents and could be precisely controlled by the concentrations of SWNT in ambient conditions. The special geometry of meniscus as the capillary bridge has not only given rise to a much higher efficiency of fabrication than what previously reported but also allowed us to monitor the pinning and depinning process carefully and further investigate the mechanism underlying the formation of different film morphologies.
In contrast with the conventional "stick-slip" model, we have provided the new dynamical pinning and zipping model for the contact line (CL) behavior. By analyzing the motion of CL and varying deposited patterns, the traditionally so-called "stick" state should be treated as a dynamical pinning process due to the interfacial tension contrast between SWNT-covered and bare silicon surface. Besides, the plausible one-step "slip" motion could be dominated by the zipping-like kink propagation.
In addition, the experiments with heated substrates at higher temperatures between 30°C and 50 °C have shown that the striped pattern could be fabricated by both much lower SWNT and SDS concentrations than that in room temperature, which is consistent with our model of interfacial tension contrast. In this situation, the deposition rate was increased but the quality of SWNT alignment was undermined because the corresponding moving velocity of SWNT was also too fast for SWNTs to rotate when the evaporative rate was high.
The similar results were identified by the SWNT/polymer conjugates dispersed in chloroform under the similar setups and other identical conditions. The typical breathing motion of dynamical pinning and zipping-like propagation for depinning were confirmed by the new suspensions despite that some morphological parameters changed dramatically compared with that from the aqueous solution. For example, the spacing between stripes reached 100 µm ~ 200 µm because the large contact angle contrast between HDMS- and SWNT-covered surface accompanies with the high evaporation rate of chloroform in the pinning and depinning process. Likewise the average CL velocity for fabrication reached around 20 µm/s due to the much higher evaporation rate of chloroform than water.
Using alike suspensions, the modified EISA method called dose-controlled floating evaporative self-assembly (DFES) was employed to implement the self-assembly of SWNTs on the water/air interface and then deposit them on solid substrate by directed floating. Although the stripes were fabricated successfully by drops with certain doses and SWNT concentrations, there inevitably existed randomly oriented SWNTs from the water surface that built networks between the stripes containing well-aligned tubes. In order to slow down the evaporation rate and monitor the process detailedly, we used chlorobenzene as the solvent instead of chloroform and find the typical pinning/depinning movement of the CL. A preliminary analysis of the results in terms of chlorobenzene implied that the CL possibly followed the similar pinning/depinning process in consistence with our model with capillary bridge.
In the last part of the thesis, the primary research on the optical properties of these stripes of ultrahigh purity semiconducting nanotubes was conducted by fluorescence microscopy and photoluminescence excitation (PLE) spectroscopy. The energy transfer of the photogenerated excitons was confirmed between different tube species with controlled band gaps.
In short, the experiments performed in this thesis allowed to gain new insights about the fabrication of large-area SWNT thin films by the cost-effective solution-processed method and most importantly to uncover its intrinsic mechanism as well. Combined with the separation and selection technique like density gradient centrifugation or polyfluorene derivatives assisted method, highly monodisperse semiconducting nanotubes could be deposited into organized, controllable and functional arrays.
Beyond the ambient conditions, precise control for the evaporation under preset temperature and vapor pressure could possibly extend the technique to the industry level. Assisted by some other mature techniques such as roll-to-roll printing, the cost-effective method could be widely used in the manufacture of various thin film devices. More complex 2D or even 3D structures could be designed and accomplished by the method for the functional or stretchable requirements. Further research on the fundamental exciton transition and diffusion in different networks or structures of SWNTs will be the significant precondition for the real applications.
Looking ahead, from the individual carbon nanotube to its thin film, this promising material with outstanding properties had many challenges to overcome before the real-world applications. Thanks to the availability of pure and well-defined materials, the scalable solution-processed approaches for fabrication of thin films should be able to unlock the potential of carbon nanotubes and exploit them in (opto-)electronic devices in the foreseeing future.
The purpose of confidence and prediction intervals is to provide an interval estimation for an unknown distribution parameter or the future value of a phenomenon. In many applications, prior knowledge about the distribution parameter is available, but rarely made use of, unless in a Bayesian framework. This thesis provides exact frequentist confidence intervals of minimal volume exploiting prior information. The scheme is applied to distribution parameters of the binomial and the Poisson distribution. The Bayesian approach to obtain intervals on a distribution parameter in form of credibility intervals is considered, with particular emphasis on the binomial distribution. An application of interval estimation is found in auditing, where two-sided intervals of Stringer type are meant to contain the mean of a zero-inflated population. In the context of time series analysis, covariates are supposed to improve the prediction of future values. Exponential smoothing with covariates as an extension of the popular forecasting method exponential smoothing is considered in this thesis. A double-seasonality version of it is applied to forecast hourly electricity load under the use of meteorological covariates. Different kinds of prediction intervals for exponential smoothing with covariates are formulated.
The scope of computational chemistry can be broadened by developing new methods and more efficient algorithms. However, the evaluation of the applicability of the methods for the different fields of chemistry is equally important. In this thesis systems with an unusual and complex electronic structure, such as excitonic states in organic semiconductors, a boron-containing bipolaron and the excited states of pyracene were studied and the applicability of the toolkit of computational chemistry was investigated. Concerning the organic semiconductors the focus was laid on organic solar cells, which are one of the most promising technologies with regard to satisfying the world's need for cheap and environmentally sustainable energy. This is due to the low production and material costs and the possibility of using flexible and transparent devices. However, their efficiency does still not live up to the expectations. Especially the exciton diffusion lengths seem to be significantly too short. In order to arrive at improved modules, a fundamental understanding of the elementary processes occurring in the cell on the molecular and supramolecular level is needed. Computational chemistry can provide insight by separating the different effects and providing models for predictions and prescreenings. In this thesis, the focus was laid on the description of excitonic states in merocyanines and perylene-based dyes taking the influence of the environment into account.
At first, the photochemical isomerization between two configurations of 6-nitro BIPS observed experimentally was studied by first benchmarking several functionals against SCS-ADC(2) in the gas phase and subsequently calculating the excited-state potential energy surface. The geometries obtained from a relaxed scan in the ground state as well as from a scan in the excited state were used. The environment was included using different polarizable continuum models. It was shown that the choice of the model and especially the question of the state specificity of the approach is of vital importance. Using the results of the calculations, a two-dimensional potential energy surface could be constructed that could be used to explain the experimental findings. Furthermore, the importance of the excited-state isomerization as a potential deactivation channel in the exciton transport was pointed out.
Then the assessment of the suitability of different merocyanines for optoelectronic applications with quantum-chemical methods was discussed. At first, the effect of the environment on the geometry, especially on the bond length alternation pattern, was investigated. It was shown that the environment changes the character of the ground-state wave function of several merocyanines qualitatively, which means that the results of gas-phase calculations are meaningless - at least when a comparison with solution or device data is desired. It was demonstrated that using a polarizable continuum model with an effective epsilon, a qualitative agreement between the calculated geometry and the geometry in the crystal structure can be obtained. Therefore, by comparing the bond length alternation in solution and in the crystal, a rough estimate of the effect of the crystal environment can be made.
It was further shown that the connection between the HOMO energy and the open-circuit voltage is not as simple as it is often implied in the literature. It was discussed that it is not clear whether the HOMO of a single molecule or a $\pi$-stack containing several monomers should be used and if the environmental charges of the bulk phase or the interface should be included. Investigating the dependence of the HOMO energy on the stack size yielded no definitive trend. Furthermore, it was discussed that the effect due the optimization of the modules (solvent, bulk heterojunction) during the production masks any potential correlation between the HOMO energy and measured open-circuit values. Therefore, a trend can only be expected for unoptimized bilayer cells. It was concluded that ultimately, the importance of the HOMO energy should not be overestimated.
The correlation between the exciton reorganization energy and the so-called cyanine limit, which is predicted by a simple two-state model, was also discussed. By referring to the results of VB calculations, it was discussed that the correlation indeed exists and is non-negligible, although the effect is not as strong as one might have expected. In this context, a potential application of a VB/MM approach was covered briefly. The importance of the molecular reorganization energy and the device morphology was also discussed.
It was concluded that the optimization of merocyanines for organic optoelectronic devices is inherently a multiparameter problem and one cannot expect to find one particular parameter, which solely controls the efficiency.
The perylene-based dyes were studied with a focus on the description of a potential trapping mechanism involving an intermolecular motion in a dimer. The aim was to find methods which can be applied to larger model systems than a dimer and take the effect of the environment into account. As a test coordinate the longitudinal shift of two monomers against each other was used. At first, it was demonstrated how the character of an excited state in a dimer can be defined and how it can be extracted from a standard quantum-chemical calculation. Then several functionals were benchmarked and their applicability or failure was rationalized using the character analysis. Two recipes could be proposed, which were applied to a constraint optimization (only intermolecular degrees of freedom) in the excited states of the PBI dimer and to the description of the potential energy surfaces of ground and excited states along a longitudinal displacement in the perylene tetramer, respectively.
It was further demonstrated that the semi-empirical OMx methods fail to give an accurate description of the excited-state potential energy surfaces as well as the ground-state surface along the test coordinate. This failure could be attributed to an underestimation of overlap-dependent terms. Consequently, it could be shown that the methods are applicable to large intermolecular distances, where the overlap is negligible. The results of DFT calculations with differently composed basis sets suggested that adding an additional single p-function for each atom should significantly improve the performance.
QM/MM methods are ideally suited to take the effect of the environment on a a dimer model system into account. However, it was shown that standard force fields also give an incorrect description of the interaction between the monomers along the intermolecular coordinate. This failure was attributed to the isotropic atom-atom interaction in the repulsion term of the Lennard-Jones potential. This was corroborated using two simple proof-of-principle anisotropy models. Therefore, a novel force field called OPLS-AA_O was presented that is based on OPLS-AA, but uses an anisotropic model for the repulsion. The model involves the overlap integral between the molecular densities, which are modeled as a sum of atom-centered p-type Gaussian functions. It was shown that using this force field an excellent agreement with the DFT results can be obtained when the correct parameters are used. These parameters, however, are not very generalizable, which was attributed to the simplicity of the model in its current state (using the same exponential parameter for all atoms). As a short excursion, the applicability of an MO-based overlap model was discussed.
It was demonstrated that the repulsion term based on the density overlap can be used to correct the failure of the OMx methods for the ground states. This is in accord with the assumption that an underestimation of the overlap terms is responsible for the failure.
It was shown that OPLS-AA_O also gives an excellent description of the longitudinal shift in a PBI tetramer. Using the tetramer as a test system and applying the recipe obtained in the TDDFT benchmark for the QM-part and OPLS-AA_O for the MM-part in conjunction with an electrostatic embedding scheme, a QM/MM description of the excited states of the PBI dimer including the effect of the environment could be obtained.
In the last chapter the theoretical description of the Bis(borolyl)thiophene dianion and the excited states of pyracene were discussed. The electronic structure of the Bis(borolyl)thiophene dianion - a negative bipolaron - was elucidated using DFT and CASPT2 methods. Furthermore, an estimation of the extent of triplet admixture to the ground state due to spin-orbit coupling was given.
In the second project the S1 and S2 states of pyracene were computed using SCS-CC2 and SCS-ADC(2) and an estimation for the balance between aromaticity and ring strain was given. This also involved computing the vibrational frequencies in the excited states.
In both studies the results of the computations were able to rationalize and complete experimental results.