Eduard Study (1862-1930) - ein mathematischer Mephistopheles im geometrischen G��rtchen

Diese Arbeit befasst sich mit Eduard Study (1862-1930), einem der deutschen Geometer um die Jahrhundertwende, der seine Zeit zum Einen durch seine Kontakte zu Klein, Hilbert, Engel, Lie, Gordan, Halphen, Zeuthen, Einstein, Hausdorff und Weyl gepr��gt hat, zum Anderen in ihr aber auch f��r seine bei��enden und stilistisch ausgefeilten Kritiken ebenso ber��hmt wie ber��chtigt war. Da sich Study mit einer Vielzahl mathematischer Themen besch��ftigt hat, f��hren wir zun��chst in die von ihm bearbeiteten Gebiete der Geometrie des 19. Jahrhunderts ein (analytische und synthetische Geometrie im Sinne von Monge, Poncelet, Pl��cker und Reye, Invariantentheorie Clebsch-Gordan'scher Pr��gung, abz��hlende Geometrie von Chasles und Halphen, die Werke Lie's und Grassmann���s, Liniengeometrie sowie Axiomatik und Grundlagenkrise). In seiner darauf folgenden Biographie finden sich als zentrale Stellen seine Habilitation bei Klein ��ber die Chasles���sche Vermutung, sein Streit mit Zeuthen dar��ber als eine der Debatten der Mathematischen Annalen (aus der er historisch zwar nicht, mathematisch aber tats��chlich als Gewinner h��tte herausgehen m��ssen, wie wir an der L��sung des Problems durch van der Waerden sehen werden) und seine Auseinandersetzungen als etablierter Bonner Professor mit Engel ��ber Lie, Weyl ��ber Invariantentheorie, zahlreichen philosophischen Richtungen ��ber das Raumproblem, Pasch���s Axiomatik, Hilbert���s Formalismus sowie Brouwer���s und Weyl���s Intuitionismus.

Mechanistic study of the effects of 8-oxo-7,8-dihydroguanine (8-oxoG) on reporter gene expression in mammalian cells

DNA damage causes replication errors, leading to genetic instability or cell death. Besides that, many types of DNA base modifications have been shown to interfere with transcriptional elongation if they are located in the transcribed DNA strand of active genes, acting as roadblocks for RNA polymerases. It is widely assumed that transcription blockage by endogenous DNA damage is responsible for the early cell senescence in organs and accelerated ageing observed in individuals with compromised nucleotide excision repair.rnThe aims of this work were to design new experimental systems for testing transcription blocking potentials of DNA base modifications in an individual gene and to apply these test systems to the investigation of the effects of a frequent endogenously generated base modification, namely 8-oxo-7,8-hydroxyguanine (8-oxoG), on the gene transcription in cells. Several experimental strategies were employed for this purpose. First, I constructed an episomal vector encoding for a short-lived EGFP-ODC fusion protein and measured expression of the reporter gene in permanently transfected clonal cell lines exposed to DNA damaging agents. Second, the expression of plasmid-borne EGFP gene damaged with photosensitisers to obtain one or several oxidative purine modifications per plasmid molecule was determined in transiently transfected human and mouse host cells in an approach known as ���host cell reactivation���. As a prerequisite for these experiments, a robust method of precise quantitative measurement of the EGFP gene expression in transiently transfected cells by flow cytometry was developed and validated. Third, I elaborated a very efficient procedure for insertion of synthetic oligonucleotides carrying 8-oxoG into plasmid DNA, avoiding any unwanted base damage and strand breaks. The consequences of 8-oxoG placed in defined positions in opposing DNA strands of the EGFP gene for transcription were measured by host cell reactivation in cells with functional 8-oxoguanine DNA glycosylase (OGG1) gene and in OGG1 null cells.rnThe results obtained in Ogg1-/- cells demonstrated that unrepaired 8-oxoG, even if situated in the transcribed DNA strand, does not have any negative effect on the reporter gene transcription. On the other hand, as few as one 8-oxoG was sufficient to cause a significant decrease of the gene expression in OGG1-proficient cell lines, i.e. in the presence of base excision repair. For two analysed positions of 8-oxoG in the plasmid DNA, the inhibition of gene transcription by the base modification correlated with the efficiency of its excision by purified OGG1 protein under cell-free conditions. Based on these findings, it has to be concluded that the observed decrease of transcription is mediated by excision of the base modification by OGG1 and probably caused by the repair-induced single-strand breaks. The mechanism of transcription inhibition by 8-oxoG is therefore clearly distinct from stalling of elongating RNA polymerase II complexes at the modified base.

Laboratory study on the optical properties of absorbing atmospheric aerosols and field applications

The interaction between aerosols and sun light plays an important role in the radiative balance of Earth���s atmosphere. This interaction is obtained by measuring the removal (extinction), redistribution (scattering), and transformation into heat (absorption) of light by the aerosols; i.e. their optical properties. Knowledge of these properties is crucial for our understanding of the atmospheric system. rn Light absorption by aerosols is a major contributor to the direct and indirect effects on our climate system, and an accurate and sensitive measurement method is crucial to further our understanding. A homebuilt photoacoustic sensor (PAS), measuring at a 532nm wavelength, was fully characterized and its functionality validated for measurements of absorbing aerosols. The optical absorption cross-sections of absorbing polystyrene latex spheres, to be used as a standard for aerosol absorption measurements, were measured and compared to literature values. Additionally, a calibration method using absorbing aerosol of known complex refractive index was presented.rn A new approach to retrieve the effective broadband refractive indices (mbroad,eff) of aerosol particles by a white light aerosol spectrometer (WELAS) optical particle counter (OPC) was achieved. Using a tandem differential mobility analyzer (DMA)-OPC system, the nbroad,eff are obtained for both laboratory and field applications. This method was tested in the laboratory using substances with a wide range of optical properties and it was used in ambient measurements to retrieve the nbroad,eff of biomass burning aerosols in a nationwide burning event in Israel. The retrieved effective broadband refractive indices for laboratory generated scattering aerosols were: ammonium sulfate (AS), glutaric acid (GA), and sodium chloride, all within 4% of literature values. For absorbing substances, nigrosine and various mixtures of nigrosine with AS and GA were measured, as well as a lightly absorbing substance, Suwannee river fulvic acid (SRFA). For the ambient measurements, the calibration curves generated from this method were to follow the optical evolution of biomass burning (BB) aerosols. A decrease in the overall aerosol absorption and scattering for aged aerosols during the day after the fires compared to the smoldering phase of the fires was found. rn The connection between light extinction of aerosols, their chemical composition and hygroscopicity for particles with different degrees of absorption was studied. The extinction cross-section (��ext) at 532nm for different mobility diameters was measured at 80% and 90% relative humidity (RH), and at an RH<10%. The ratio of the humidified aerosols to the dry ones, fRHext(%RH,Dry), is presented. For purely scattering aerosols, fRHext(%RH,Dry) is inversely proportional with size; this dependence was suppressed for lightly absorbing ones. In addition, the validity of the mixing rules for water soluble absorbing aerosols is explored. The difference between the derived and calculated real parts of the complex RIs were less than 5.3% for all substances, wavelengths, and RHs. The obtained imaginary parts for the retrieved and calculated RIs were in good agreement with each other, and well within the measurement errors of retrieval from pulsed CRD spectroscopy measurements. Finally, a core-shell structure model is also used to explore the differences between the models, for substances with low growth factors, under these hydration conditions. It was found that at 80% RH and for size parameters less than 2.5, there is less than a 5 % difference between the extinction efficiencies calculated with both models. This difference is within measurement errors; hence, there is no significant difference between the models in this case. However, for greater size parameters the difference can be up to 10%. For 90% RH the differences below a size parameter of 2.5 were up to 7%.rn Finally, the fully characterized PAS together with a cavity ring down spectrometer (CRD), were used to study the optical properties of soot and secondary organic aerosol (SOA) during the SOOT-11 project in the AIDA chamber in Karlsruhe, Germany. The fresh fractal-like soot particles were allowed to coagulate for 28 hours before stepwise coating them with SOA. The single scattering albedo for fresh fractal-like soot was measured to be 0.2 (��0.03), and after allowing the soot to coagulate for 28 hours and coating it with SOA, it increased to 0.71(��0.01). An absorption enhancement of the coated soot of up to 1.71 (��0.03) times from the non-coated coagulated soot was directly measured with the PAS. Monodisperse measurements of SOA and soot coated with SOA were performed to derive the complex refractive index (m) of both aerosols. A complex refractive index of m = 1.471(��0.008) + i0.0(��0.002) for the SOA-��O3 was retrieved. For the compact coagulated soot a preliminary complex refractive index of m = 2.04(+0.21/-0.14) + i0.34(+0.18/-0.06) with 10nm(+4/-6) coating thickness was retrieved.rn These detail properties can be use by modelers to decrease uncertainties in assessing climatic impacts of the different species and to improve weather forecasting.rn

Mechanistic study of cell death induction by O 6-methylating agents, focusing on the role of homologous recombination as a molecular target for sensitization of tumor cells to chemotherapeutic alkylating agents

Chemotherapeutic SN1���methylating agents are important anticancer drugs. They induce several covalent modifications in the DNA, from which O6���methylguanine (O6MeG) is the main toxic lesion. In this work, different hypotheses that have been proposed to explain the mechanism of O6MeG���triggered cell death were tested. The results of this work support the abortive processing model, which states that abortive post���replicative processing of O6MeG���driven mispairs by the DNA mismatch repair (MMR) machinery results in single���strand gaps in the DNA that, upon a 2nd round of DNA replication, leads to DNA��double���strand break (DSB) formation, checkpoint activation and cell death. In this work, it was shown that O6MeG induces an accumulation of cells in the 2nd G2/M���phase after treatment. This was accompanied by an increase in DSB formation in the 2nd S/G2/M���phase, and paralleled by activation of the checkpoint kinases ATR and CHK1. Apoptosis was activated in the 2nd cell cycle. A portion of cells continue proliferating past the 2nd cell cycle, and triggers apoptosis in the subsequent generations. An extension to the original model is proposed, where the persistence of O6MeG in the DNA causes new abortive MMR processing in the 2nd and subsequent generations, where new DSB are produced triggering cell death. Interestingly, removal of O6MeG beyond the 2nd generation lead to a significant, but not complete, reduction in apoptosis, pointing to the involvement of additional mechanisms as a cause of apoptosis. We therefore propose that an increase in genomic instability resulting from accumulation of mis���repaired DNA damage plays a role in cell death induction. Given the central role of DSB formation in toxicity triggered by chemotherapeutic SN1���alkylating agents, it was aimed in the second part of this thesis to determine whether inhibition of DSB repair by homologous recombination (HR) or non���homologous end joining (NHEJ) is a reasonable strategy for sensitizing glioblastoma cells to these agents. The results of this work show that HR down���regulation in glioblastoma cells impairs the repair of temozolomide (TMZ)���induced DSB. HR down���regulation greatly sensitizes cells to cell death following O6���methylating (TMZ) or O6���chlorethylating (nimustine) treatment, but not following ionizing radiation. The RNAi mediated inhibition in DSB repair and chemo���sensitization was proportional to the knockdown of the HR protein RAD51. Chemo���sensitization was demonstrated for several HR proteins, in glioma cell lines proficient and mutated in p53. Evidence is provided showing that O6MeG is the primary lesion responsible for the increased sensitivity of glioblastoma cells following TMZ treatment, and that inhibition of the resistance marker MGMT restores the chemo���sensitization achieved by HR down���regulation. Data are also provided to show that inhibition of DNA���PK dependent NHEJ does not significantly sensitized glioblastoma cells to TMZ treatment. Finally, the data also show that PARP inhibition with olaparib additionally sensitized HR down���regulated glioma cells to TMZ. Collectively, the data show that processing of O6MeG through two rounds of DNA replication is required for DSB formation, checkpoint activation and apoptosis induction, and that O6MeG���triggered apoptosis is also executed in subsequent generations. Furthermore, the data provide proof of principle evidence that down���regulation of HR is a reasonable strategy for sensitizing glioma cells to killing by O6���alkylating chemotherapeutics.

The formation of OH radicals from Criegee intermediates: a LIF-FAGE study from laboratory to ambient

Das Hydroxyl Radikal ist, auf globalem Ma��stab, das bedeutendste Oxidant in der Atmosph��re. Es initiiert den Abbauprozess vieler, teilweise sch��dlicher, Spurengase und insbesondere den von fl��chtigen Kohlenwasserstoffen (VOC). Die OH Konzentration ist somit ein gutes Ma�� f��r die augenblickliche Selbstreinigungskapazit��t der Atmosph��re. Messungen zu n��chtlicher Zeit mit LIF-FAGE-Instrumenten (engl.: laser-induced fluorescence - fluorescence assay by gas expansion) haben Konzentrationen des Hydroxylradikals (OH) ergeben, die signifikant h��her waren, als sich mit der bekannten Chemie erkl��ren lie��. Um herauszufinden, ob ein solches Signal wirklich atmosph��risches OH ist oder von einer st��renden Spezies stammt, die im Messinstrument OH produziert, wurde das LIF-FAGE-Instrument des Max-Planck-Instituts f��r Chemie (MPIC) im Rahmen dieser Doktorarbeit modifiziert und getestet. Dazu wurde ein so genannter Inlet Pre-Injector (IPI) entwickelt, mit dem in regelm����igen Abst��nden ein OH-F��nger in die Umgebungsluft abgegeben werden kann, bevor das OH vom Instrument erfasst wird. Mit dieser Technik ist es m��glich, ein Hintergrund-OH (OHbg), d. h. ein im Instrument erzeugtes OH-Signal, vom gemessenen OH-Gesamtsignal (OHtot) zu trennen. Die Differenz zwischen OHtot und OHbg ist die atmosph��rische OH-Konzentration (OHatm). Vergleichsmessungen mit der hier entwickelten Technik, dem IPI, in zwei verschiedenen Umgebungen mit Instrumenten basierend auf Massenspektrometrie mit chemischer Ionisation (CIMS, engl.: chemical ionization mass spectrometry) als alternativer Methode des OH-Nachweises, zeigten eine weitgehende ��bereinstimmung. Eine umfassende Beschreibung des Systems zur Ermittlung der Ursache des OHbg hat ergeben, dass es weder von einem Artefakt des Instruments noch von hinl��nglich bekannten und beschriebenen LIF-FAGE-Interferenzen stammt. Zur Bestimmung der Spezies, die das OHbg-Signal verursacht, wurden verschiedene Laborstudien durchgef��hrt. Die Arbeit im Rahmen dieser Doktorarbeit hat ergeben, dass das LIF-FAGE-Instrument leicht auf OH reagiert, das beim monomolekularen Zerfall stabilisierter Criegee-Intermediate (SCI) im Niederdruckbereich des Instruments gebildet wird. Criegee-Intermediate oder Carbonyloxide entstehen bei der Ozonolyse unges��ttigter fl��chtiger Kohlenwasserstoffverbindungen (VOC, engl.: volatile organic compounds) und k��nnen daher in der Umgebungsluft vorkommen. Anhand von Tests mit verschiedenen Verweilzeiten der SCI im Niederdruckbereich des Instruments in Verbindung mit einem detaillierten Modell mit der neuesten SCI-Chemie wurde die monomolekulare Zerfallsgeschwindigkeit von 20 ��� 10 s-1 f��r den syn-Acetaldehyd-Oxykonformer bestimmt. Der in Feldkampagnen gemessene OHbg-Wert wurde dahingehend untersucht, ob SCI die Quelle des beobachteten Hintergrund-OH im Feld sein k��nnten. Das Budget f��r die SCI-Konzentration, das f��r die Kampagnen HUMPPA-COPEC 2010 und HOPE 2012 berechnet wurde, ergab eine SCI-Konzentration zwischen ca. 103 und 106 Molek��len pro cm3. In der Kampagne HUMPPA-COPEC 2010 ergab die Schwefels��urekonzentration, dass die OH-Oxidation von SO2 allein die gemessene H2SO4-Konzentration nicht erkl��ren konnte. In dieser Arbeit konnte gezeigt werden, dass das Hintergrund-OH mit dieser ungekl��rten Produktionsrate von H2SO4 korreliert und somit die Oxidation von SO2 durch SCI als m��gliche Erkl��rung in Frage kommt. Ferner korreliert das Hintergrund-OH in der Kampagne HOPE 2012 mit dem Produkt aus Ozon und VOC und konnte mit SO2 als SCI F��nger entfernt werden. Qualitativ zeigen wir somit, dass das in der Umgebungsluft gemessene Hintergrund-OH wahrscheinlich durch den monomolekularen Zerfall von SCI verursacht wird, doch sind weitere Studien notwendig, um die quantitativen Beziehung f��r diese Spezies und dem Hintergrund-OH in unserem Instrument zu bestimmen.