Flavonoids are a class of plant metabolites with C6-C3-C6 structure responsible for many biological functions, including coloration and defense. Citrus paradisi, grapefruit, contains a wide variety of flavonoids which are grouped by the extent of modification, examples of which are flavonols, flavones, and flavanones. A major modification is the addition of glucose by glucosyltransferases (GTs) to stabilize the structure and provide ease of transport. This process can be highly substrate and regiospecific. With Cp3OGT, glucose is added at the 3-hydroxy position. This 3GT only accepts flavonols as its substrate; however, a Vitis vinifera (grape) 3-GT can accept both flavonols and anthocyanidins. Homology modeling using the crystallized structure of the V. vinifera GT predicted sites of amino acids that could influence substrate binding site. The 382 position was of particular interest with arginine in C. paradisi and tryptophan in V. vinifera. This change is hypothesized to cause a shift in substrate specificity of the Cp3OGT to accept anthocyanidins as well as flavonols. Site-directed mutagenesis was performed to form the R382W mutant Cp3OGT and transformed into yeast for expression. Western blot determined the optimal protein induction period for the cells, after which the cells were broken to extract the recombinant mutant protein. Purification of the R382W 3GT allowed for enzyme analysis to be performed by measuring the incorporation of radioactive glucose into the reaction product. HPLC will be used to identify reaction products. An enzyme kinetics study will show the extent of any biochemical change in function as a result of this mutation; results will then be incorporated into a refined protein model.

The Common Core State Standards and the National Council for the Social Studies (C3 Framework) have recently prompted renewed emphasis on literacy, particularly in history, therefore it is important to analyze and compare what exactly the teacher educators of leading journals are saying about historical literacy. This study examines the literacy messages for the history classroom in The Journal of Adolescent and Adult Literacy and Theory (JAAL) and Research in Social Education (TRSE) from 2010-2015. An emergent, qualitative content analysis was used to analyze data from these journals. Results from this study indicates definitions on historical literacy vary between journals, both journals focused on elements of historical literacy over the whole concept, and historical literacy is addressed differently for distinctive intended participants. Implications from this study concerning teacher educators and history teachers are examined and possibilities for further research are also discussed.

Several studies have shown that complement and thrombotic events co-exist. Platelets have been suspected to act as the bridge between the two cascade systems. To study the platelet-induced complement activation we developed a system in which platelets were activated by thrombin receptor activating peptide (TRAP) in platelet rich plasma (PRP) or whole blood anti-coagulated using the specific thrombin inhibitor, lepirudin. TRAP-activated platelets induced a fluid-phase complement activation measured as generation of C3a and sC5b-9, triggered by released chondroitin sulphate-A (CS-A) which interacted with C1q and activated the complement system through the classical pathway. Complement components C1q, C3, C4 and C9 were also shown to bind to TRAP-activated platelets but this binding did not seem to be due to a complement activation since blocking of complement activation at the C1q or C3 levels did not affect the binding of the complement proteins. The C3 which bound to activated platelets consisted of C3(H2O), indicating that bound C3 was not proteolytically activated. Binding of C1q was partially dependent on CS-A exposure on activated platelets. The abolished complement activation on the surface of activated platelets was suggested to be dependent on the involvement of several complement inhibitors. We confirmed the binding of C1INH and factor H to activated platelets. To this list we have added another potent complement inhibitor, C4BP. The binding of factor H and C4BP was shown to be dependent on exposure of CS-A on activated platelets. The physiological relevance of these reactions was reflected in an elevated expression of CD11b on leukocytes, and increased generation of platelet-leukocyte complexes. The platelets were involved in these events by at least two different mechanisms; generation of C5a which activated leukocytes and binding of C3(H2O)/iC3(H2O), a ligand to the intergrin CD11b/CD18 on their surface. These mechanisms add further to the understanding of how platelets interact with the complement system and will help us to understand the role of the complement system in cardiovascular disease and thrombotic conditions. / Platelet Mediated Complement Activation

Using ion-trapping techniques, selected laboratory experiments on ion-molecule reactions of astrophysical interest have been performed. For the first time a carbon beam source has been integrated into an ion trapping machine for studying collisions between ions and neutral carbon atoms and molecules. Results are presented for the interaction of D3+ ions stored in a ring-electrode trap (RET), with a beam of hot neutral carbon molecules, Cn (n = 1, 2, 3). The measured reaction rate coefficients are up to a factor two smaller than values presently used in astrophysical models. In order to complete our knowledge about the ion chemistry involving three carbon atoms, detailed investigations of reactions of C3+, C3H+ and C3H3+ with H2 and HD have been performed between 15 K and room temperature. These studies have been performed in a second apparatus, a variable-temperature 22-pole trap machine (VT-22PT). Results include reactive collisions, deuteration and radiative association. It is discussed in connection with the increase in lifetime of the C3+ + H2 collision complexes with falling temperature, what could be responsible for producing more C3H+ at 15 K. Tunneling is excluded. In C3+ + HD collisions an isotope effect has been detected, the C3D+ product ions being slightly more abundant than C3H+. Comparison of the reaction of C3H+ primary ions with HD and H2 gas revealed that the deuterated molecules are significantly more reactive. The process of radiative association of C3H+ and for the first time of C3+ with hydrogen molecules has been observed. An analysis of the data shows that radiative association becomes slower, if the neutral reactant is deuterated. Finally, the theoretical prediction from ab initio calculations that C3H3+ does not exchange an H for a D in collisions with HD, has been proven in an ion trap experiment. Careful analysis of all competing processes allows the conclusion that the rate coefficient is smaller than 4x10-16 cm3s-1 at 15 K. / Unter Verwendung von zwei Speicherapparaturen wurden ausgewählte, astrophysikalische wichtige Ionen-Molekülreaktionen untersucht. Durch die Kombination einer Kohlenstoffquelle mit einem Ionenspeicher, in dem so Reaktionen zwischen Ionen und Kohlenstoffmolekülen oder -atomen untersucht werden können, wurde Neuland betreten. Es werden Ergebnisse vorgestellt für die Reaktion von D3+ Ionen, die in einem Ringelektrodenspeicher gefangen sind, mit einem Strahl von heißen Cn (n = 1, 2, 3). Die gemessenen Ratenkoeffizienten sind nur halb so groß wie die Werte, die in astrophysikalischen Modellen verwendet werden. Um die Kenntnis über alle möglichen Reaktionen, bei denen drei C-Atome beteiligt sind, abzurunden, wurden zwischen 15 K und Zimmertemperatur die Reaktionen zwischen C3+, C3H+ und C3H3+ Ionen mit H2 und HD in vielen Details untersucht. Diese Experimente wurden in einer zweiten Apparatur durchgeführt, in der ein temperaturvariabler 22-Polspeicher das zentrale Element ist (VT-22PT). Berichtet werden Ergebnisse zu reaktiven Stößen, zur Deuterierung von Kohlenwasserstoffen und zur Strahlungsassoziation. In der Diskussion bleibt offen, was - in Verbindung mit der von 300 K zu 15 K zunehmenden Lebensdauer - der Grund dafür sein kann, daß die Bildung des exothermen Produkts C3H+ anwächst. Der Tunneleffekt scheidet aus. Bei der Reaktion C3+ + HD wurde ein Isotopeneffekt beobachtet, das C3D+ Produkt wird etwas häufiger gebildet als C3H+. Ein Vergleich der Reaktion zwischen C3H+ Ionen mit HD bzw. H2 zeigt, daß das deuterierte Molekül wesentlich reaktiver ist. Es wurden Ratenkoeffizienten für die Strahlungsassoziation von H2 Molekülen mit C3H+ und erstmals mit C3+ Ionen gemessen. Die Auswertung der Daten zeigt, dass der Prozeß langsamer abläuft, wenn der neutrale Stoßpartner deuteriert ist. Schließlich wurde experimentell die theoretische Vorhersage überprüft, dass C3H3+ keinen H-D Austausch mit HD eingeht. Eine sorgfältige Analyse aller konkurrierenden Prozesse ergab, dass bei 15 K der Raten koeffizient kleiner als 4x10-16 cm3s-1 ist.

Records of change of [delta]13C values in vertebrate teeth offer an opportunity to gain insight into changes in past vegetation. Increasingly, teeth from small mammals are used for such purposes, but because their teeth grow very rapidly, seasonal changes in vegetation potentially provide a large source of variability in carbon isotope composition, complicating interpretations of small mammal tooth isotope data. To investigate the controls of seasonality on the stable isotope composition of fossil teeth, we constructed a Monte-Carlo-based model to simulate the effects of changes in the seasonal pattern of diet in leporid lagomorphs (rabbits and hares) on the distribution of [delta]¹³C values in random populations of leporid teeth from the Edwards Plateau in central Texas. Changes in mean-state, seasonal vegetation range, and relative season length manifest themselves in predictable ways in the median, standard deviation, and skewness of simulated tooth [delta]¹³C populations, provided sufficient numbers of teeth are analyzed. This Monte Carlo model was applied to the interpretation of a 20,000 year record of leporid tooth [delta]¹³C values from Hall's Cave on the Edwards Plateau in central Texas. Variations in the [delta]¹³C values of teeth deposited at the same time (standard deviation = 1.69%) are larger than changes in the mean vegetation composition reconstructed from bulk organic carbon [delta]¹³C, indicating the influence of short-term variability, making it difficult to assess changes in mean C3/C4 vegetation from the tooth [delta]¹³C data. However, populations of teeth from different climate intervals (e.g., the late Glacial, Younger Dryas, and the Holocene) display changes in the shape of the tooth [delta]¹³C distributions. Interpretation of these changes as shifts in seasonal vegetation patterns that are based upon results from our model are consistent with hypothesized climatic changes. An increase in the standard deviation of the tooth population between the late Glacial and the Younger Dryas -- Holocene is consistent with an increase in seasonality. Furthermore, a shift to more C3-dominated vegetation in the tooth [delta]¹³C distribution during the Younger Dryas is accompanied by a more skewed population -- indicative of not only wetter conditions but an increase in the duration in the C3 growing season. However, late Holocene changes in vegetation are not clear in the tooth data, despite the evidence from bulk organic carbon [delta]¹³C values for an increase in % C3 vegetation of 57%. Small mammal teeth can potentially provide unique insights into climate and vegetation on seasonal and longer timescales that complement other data, but should be interpreted with a careful consideration of local conditions, taxon ecology and physiology, and the dominant timescales of isotope variability. / text

Made available in DSpace on 2014-06-11T19:32:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-02-03Bitstream added on 2014-06-13T19:22:04Z : No. of bitstreams: 1 marchese_ja_dr_botfca.pdf: 1209124 bytes, checksum: 3852bccf50e18f3028e21b50674aba78 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Artemisia annua L. (Asteraceae) é uma planta herbácea altamente aromática, nativa da Ásia e aclimatada no Brasil. As folhas são fonte abundante de artemisinina, uma lactona sesquiterpênica que, conjuntamente aos seus derivados semi-sintéticos, apresentam ação efetiva contra as cepas resistentes das espécies de Plasmodium causadoras da malária. Os objetivos deste trabalho foram identificar o mecanismo fotossintético e avaliar o efeito de diferentes condições de temperatura e fotoperíodo no crescimento e desenvolvimento do acesso CPQBA 2/39x1V de A. annua. Para identificar o mecanismo fotossintético foram realizados experimentos para determinar composição dos isótopos do carbono (d 13C) e a anatomia foliar associada a testes histoquímicos. Para avaliar o efeito da temperatura e fotoperíodo no crescimento e desenvolvimento de A. annua foram realizados dois experimentos em câmaras fotoperiódicas (o primeiro com temperaturas médias máx. de 37ºC e mín. de 19ºC e o segundo com máx. de 29ºC e mín. de 13ºC) e um experimento com 6 épocas de plantio em campo no município de Pato Branco-PR (26º11' S, 52º36' W e 760 m de altitude), sul do Brasil. Um último experimento realizado, foi a aplicação exógena de artemisinina em plantas de A. annua para verificar o papel da molécula na indução do florescimento. Como resultados, A. annua apresentou uma d 13C - 31.76 l 0.07, valor típico de espécies com mecanismo fotossintético C3, que apresentam em média valores de d 13C - 28. Os estudos da anatomia foliar e testes histoquímicos confirmaram os resultados encontrados para a d 13C, onde, a despeito da existência de células parenquimáticas formando um anel ao redor do feixe vascular, estas não apresentaram cloroplastos e amido, confirmando ser A. annua uma espécie de mecanismo... / Leaves of Artemisia annua L. are a plentiful source of artemisinin, a drug with proven effectiveness against malaria. One of the objectives of this work was to identify the photosynthetic type of A. annua through studies of the carbon isotope composition (d 13C) and the leaf anatomy. We also verified the growth and development of the CPQBA 2/39x1V accession under moist subtropical climate. Two experiments were carried out in greenhouse using photoperiodic chambers. The plants were submitted to photoperiods of 7, 9, 11, 13, 15 and 17 h, in two natural conditions of temperature: spring/summer (maximum of 37ºC and minimum of 19ºC) and autumn/winter (maximum of 29ºC and minimum of 13ºC). Another experiment with different planting dates at field was carried out in Pato Branco, PR (26º11' S, 52º36' W and 760 m), Southern part of Brazil. The last experiment was the application of artemisinin (0, 500, 5000, and 10000 mg L-1) in A. annua plants to verify the role of the molecule on the flowering induction. A. annua presented a d 13C - 31.76 l 0.07, what characterizes it as typical species with a C3 photosynthetic mechanism, with an average of d 13C- 28, while C4 species possess an average of d 13C - 14. The study of A. annua leaf anatomy confirms the results of d 13C, where, in spite of the existence of parenchymatic cells forming a different sheath surrounding of the vascular tissue, these cells do not have chloroplast or starch. These features do not describe the Kranz anatomy typical of C4 species. The application of artemisinin did not induce the flowering of A. annua at any of the concentrations used. The results suggest that the accumulation of the artemisinin in the pre-flowering and flowering phases in A. annua is not the physiological signal of floral induction in this species...

De tekniska system som stödjer ledning av arméns brigader har ökat i komplexitet och användbarheten har minskat. Det tar längre tid att utbilda den personal som ska hantera systemen idag jämfört med för tio år sedan. I uppsatsen har utvecklingen av ledningsstödsystem studerats med utgångspunkt i ramverken Systems Engineering och Human Factors Integration. HFI syftar till att sätta användaren i fokus för utvecklingen, snarare än tekniken som sådan. Det empiriska materialet utgörs av intervjuer med nyckelpersoner, målsättningsdokument för tekniska system och andra styrdokument som påverkar området. Studien indikerar att Försvarsmaktens förändrade inriktning mot internationella insatser under 00-talet har varit utgångspunkten för de tekniska lösningar som idag ska användas i det nationella försvaret. De krav som ställts på systemens tekniska funktioner har varit överordnade kraven på att ledningsförbandens soldater, utan tillgång till kvalificerat tekniskt stöd, ska kunna hantera systemen effektivt. Det finns skäl att anta att ett ökat fokus på HFI under systemutvecklingen skulle leda till system med bättre balans mellan teknik och människa, som i sin tur skulle leda till både ökad användbarhet och minskade kostnader. I uppsatsen föreslås några konkreta åtgärder som kan vara föremål för vidare studier och utvärdering. / The technical systems supporting command, control and communications (C3) of Swedish army brigades have increased in complexity and their usability has been reduced. The training of signal unit personnel takes longer today compared to ten years ago. In this paper the development of C3 support systems has been studied from a Systems Engineering and Human Factors Integration point of view. The aim of HFI is to put the user in the center of development instead of the technology as such. The empirical material consists of interviews, system requirements documents and other policy documents affecting the army C3 domain.The study indicates that the origin of the technical solutions for national defense use of today was the Swedish Armed Forces’ changed orientation towards international peace support operations during the century’s first decade. The requirements for technical functionality have been superior to the requirement that signal unit soldiers, without access to qualified technical support, must be able to effectively manage the systems. There is reason to assume that an increased HFI focus in system development would lead to systems with better balance between technology and humans, which in turn would increase usability and reduce cost. The paper suggests some actions that might be subject to further studies and evaluation.

Magister Scientiae (Biodiversity and Conservation Biology) / Fog and dew interception and utilization by plant canopies remains one of the least considered aspects of vegetation studies at any scale yet the few studies that have been conducted point to their considerable influence on ecological processes and a critical role in modulating climate in southern African arid ecosystems. Their relevance to succulent plant hydrology was investigated in this study.The first study measured stable 18O and 2H isotope ratios in samples of rain, fog and dew water and compared these with those assayed monthly in stem xylem water of six succulent shrub species over a one year period. Negative 18O and 2H ratios were observed in the stem xylem water of all six species signifying a predominance of water derived from fog and dew precipitation which was most conspicuous during the wet winter. This implied that fog and dew are even more important sources of water than rain and corroborated by significant correspondence found between fog and dew frequencies, succulent foliar water contents and quantum yields of photochemistry.The second study monitored variations in stem diameter at 2-hourly intervals in 8 succulent shrub species of diverse growth form over a 9-month period. Two groups of species were distinguished based on whether their daily amplitudes in stem diameter were consistently positively correlated with daily fluxes in vapour pressure deficit, which were indicative of a persistent CAM photosynthetic mode, or intermittently correlated with daily fluxes in vapour pressure deficit, which were indicative of mixed CAM and C3 photosynthetic modes. Among species displaying a persistent CAM photosynthetic mode, high nocturnal fog and dew precipitation amounts corresponded with low daily amplitudes in stem diameter, and vice versa, which pointed to reduced nocturnal stomatal water loss. These patterns, which were indistinct among species displaying mixed CAM and C3 photosynthetic modes, were corroborated by small daily amplitudes in stem diameter also consistently observed in one species displaying a CAM photosynthetic mode in ambient than artificially fog and dew excluded environments.The third study monitored changes in water mass at hourly intervals of quartz gravel substrates with different dwarf succulent species assemblages over an 8-month period.Consistently greater net amounts of water were intercepted daily by quartz gravel substrates containing Agyroderma pearsonii than Cephalophylum spissum plants as well as those without plants. These attributed to a high water repellence of A. pearsonii leaves and less radiation absorbed by the paler silvery to grey-green leaves of A. pearsonii leaves than the dark green leaves of C. spissum resulting in lower leaf temperatures and less water loss by transpiration. Quartz gravel soils devoid of plants intercepted nearly 5-times greater amounts of precipitation contributed by fog and dew than that contributed by rain. These precipitation amounts exceeding the high percentages of total hydrological input contributed by fog and dew reported in other ecosystems.The study concludes that fog and dew are a vital source of water for succulent shrubs in arid South African ecosystems and imply that diminished fog and dew frequencies associated with elevated night time temperatures accompanying global warming could exacerbate plant drought stress.

Using ion-trapping techniques, selected laboratory experiments on ion-molecule reactions of astrophysical interest have been performed. For the first time a carbon beam source has been integrated into an ion trapping machine for studying collisions between ions and neutral carbon atoms and molecules. Results are presented for the interaction of D3+ ions stored in a ring-electrode trap (RET), with a beam of hot neutral carbon molecules, Cn (n = 1, 2, 3). The measured reaction rate coefficients are up to a factor two smaller than values presently used in astrophysical models. In order to complete our knowledge about the ion chemistry involving three carbon atoms, detailed investigations of reactions of C3+, C3H+ and C3H3+ with H2 and HD have been performed between 15 K and room temperature. These studies have been performed in a second apparatus, a variable-temperature 22-pole trap machine (VT-22PT). Results include reactive collisions, deuteration and radiative association. It is discussed in connection with the increase in lifetime of the C3+ + H2 collision complexes with falling temperature, what could be responsible for producing more C3H+ at 15 K. Tunneling is excluded. In C3+ + HD collisions an isotope effect has been detected, the C3D+ product ions being slightly more abundant than C3H+. Comparison of the reaction of C3H+ primary ions with HD and H2 gas revealed that the deuterated molecules are significantly more reactive. The process of radiative association of C3H+ and for the first time of C3+ with hydrogen molecules has been observed. An analysis of the data shows that radiative association becomes slower, if the neutral reactant is deuterated. Finally, the theoretical prediction from ab initio calculations that C3H3+ does not exchange an H for a D in collisions with HD, has been proven in an ion trap experiment. Careful analysis of all competing processes allows the conclusion that the rate coefficient is smaller than 4x10-16 cm3s-1 at 15 K. / Unter Verwendung von zwei Speicherapparaturen wurden ausgewählte, astrophysikalische wichtige Ionen-Molekülreaktionen untersucht. Durch die Kombination einer Kohlenstoffquelle mit einem Ionenspeicher, in dem so Reaktionen zwischen Ionen und Kohlenstoffmolekülen oder -atomen untersucht werden können, wurde Neuland betreten. Es werden Ergebnisse vorgestellt für die Reaktion von D3+ Ionen, die in einem Ringelektrodenspeicher gefangen sind, mit einem Strahl von heißen Cn (n = 1, 2, 3). Die gemessenen Ratenkoeffizienten sind nur halb so groß wie die Werte, die in astrophysikalischen Modellen verwendet werden. Um die Kenntnis über alle möglichen Reaktionen, bei denen drei C-Atome beteiligt sind, abzurunden, wurden zwischen 15 K und Zimmertemperatur die Reaktionen zwischen C3+, C3H+ und C3H3+ Ionen mit H2 und HD in vielen Details untersucht. Diese Experimente wurden in einer zweiten Apparatur durchgeführt, in der ein temperaturvariabler 22-Polspeicher das zentrale Element ist (VT-22PT). Berichtet werden Ergebnisse zu reaktiven Stößen, zur Deuterierung von Kohlenwasserstoffen und zur Strahlungsassoziation. In der Diskussion bleibt offen, was - in Verbindung mit der von 300 K zu 15 K zunehmenden Lebensdauer - der Grund dafür sein kann, daß die Bildung des exothermen Produkts C3H+ anwächst. Der Tunneleffekt scheidet aus. Bei der Reaktion C3+ + HD wurde ein Isotopeneffekt beobachtet, das C3D+ Produkt wird etwas häufiger gebildet als C3H+. Ein Vergleich der Reaktion zwischen C3H+ Ionen mit HD bzw. H2 zeigt, daß das deuterierte Molekül wesentlich reaktiver ist. Es wurden Ratenkoeffizienten für die Strahlungsassoziation von H2 Molekülen mit C3H+ und erstmals mit C3+ Ionen gemessen. Die Auswertung der Daten zeigt, dass der Prozeß langsamer abläuft, wenn der neutrale Stoßpartner deuteriert ist. Schließlich wurde experimentell die theoretische Vorhersage überprüft, dass C3H3+ keinen H-D Austausch mit HD eingeht. Eine sorgfältige Analyse aller konkurrierenden Prozesse ergab, dass bei 15 K der Raten koeffizient kleiner als 4x10-16 cm3s-1 ist.

For the astrophysically relevant molecules, C3 and C6, ab initio calculations are performed to study the geometries of different neutral isomers, the electronic structures of C3 in its ground and excited states, and possible pathways for the reaction C3 + C3 = C6. For C3 we present calculations for the potential energy surfaces of C3 in different electronic configurations, including the singlet ground state, the triplet ground state, and some higher excited states. The geometries studied include triangular shapes with two identical bond lengths, but different bond angles between them. For the singlet and triplet ground states in the linear geometry, the total energies resulting from the mixed density functional-Hartree-Fock and quadratic configuration interaction methods reproduce the experimental values, i.e. the triplet occurs 2.1 eV above the singlet. In the geometry of an equilateral triangle, we find a low-lying triplet state with an energy of only 0.8 eV above the energy of the singlet in the linear configuration, so that the triangular geometry yields the lowest excited state of C3. For the higher excited states up to about 12 eV above the ground state, we apply time-dependent density functional theory. Even though the systematic error produced by this approach is of the order of 0.4 eV, the results give new insight into the potential energy landscape for higher excitation energies. For C6 we consider the known linear states and the lowest state of monocyclic ring. The potential energy surfaces, were built for various pathways for the reaction C3 + C3 = C6. For this investigation we apply a mixed density functional-Hartree-Fock method which gives good results with respect to the experimental values and does not demand much computational time. We have considered collinear and symmetric non-linear as well as some non-symmetric collision schemes of two C3 subunits, producing the 1Ag states of a D2h isomer, one in a cyclic shape, the other in the form of two triangles connected by the corners, and for the non-symmetric scheme the 1A' state of a Cs isomer. To investigate the pathways for the creation of C6 from two C3 we emphasize the importance of the electron configuration for the reacting C3 subunits. As a result we have obtained the following rule: The stable linear as well as the cyclic C6 molecule can only be created in the case when at least one C3 has a partially filled orbital, requiring an excited state with respect to the singlet ground state of C3. / Für die astrophysikalisch bedeutenden Moleküle C3 und C6 werden ab initio Berechnungen von elektronischen Zuständen verschiedener Isomere durchgeführt. Basierend auf der Optimierung verschiedener neutraler Isomere von C3 im Grundzustand und mehreren angeregten Zuständen werden mögliche Wege für die Reaktion C3 + C3 = C6 studiert. Für C3 werden ab initio Berechnungen für die Flächen der potentiellen Energie in verschiedenen elektronischen Konfigurationen durchgeführt, einschließlich des Singulett-Grundzustands, des Triplett-Grundzustands, und einiger höherer Anregungszustände. Die untersuchten Geometrien schließen gleichschenklige Dreiecke mit zwei identischen Bindungslängen ein, wobei der Bindungswinkel dazwischen variiert wird. Die Gesamtenergien, die sich in einem gemischten Hartree-Fock-Dichtefunktional-Verfahren und unter Verwendung der quadratischen Konfigurationswechselwirkung ergeben, reproduzieren die experimentell beobachtete Energiedifferenz von 2.1 eV zwischen dem niedrigsten Triplett-Zustand und dem Singulett-Grundzustand. In der Geometrie des gleichseitigen Dreiecks ergibt sich ein niedrigerliegender Triplett-Zustand mit einer Energie von nur 0.8 eV über der Energie des Singuletts im linearen Isomer, so dass die dreieckige Geometrie den niedrigsten Anregungszustand von C3 ergibt. Für höhere Anregungsenergien bis zu 12 eV über dem Grundzustand wird zeitabhängige Dichtefunktional-Theorie zur Ermittlung der Energie angeregter elektronischer Konfigurationen eingesetzt. Obwohl der von dieser Methode produzierte systematische Fehler von der Größenordnung von 0.4 eV ist, ergeben sich interessante neue Einblicke in die Potentiallandschaft angeregter Zustände. Für C6 betrachten wir das bekannte lineare Isomer und das zyklische Isomer. Der Verlauf der Potentialoberflächen wird für verschiedene Reaktionspfade C3+C3 = C6 untersucht, wobei ein gemischtes Hartree-Fock-Dichtefunktional-Verfahren einesetzt wird. Im Mittelpunkt des Interesses stehen dabei kollineare Anordnungen linearer C3 Moleküle, symmetrische Kollisionen nichtlinearer Reaktanden, sowie einige nichtsymmetrische koplanare Geometrien des Zusammenstosses zweier linearer Moleküle. Als Ergebnis der Reaktionen mit symmetrischen Anordnungen ergibt sich lineares C6 oder zyklisches C6 mit D2h Symmetrie in einem elektronischen Zustand der höchsten Symmetrie 1Ag. Das nicht-symmetrische Reaktionsschema führt zu einem planaren Isomer Cs im Zustand 1A'. Um die Wege für die Bildung von C6 aus zwei C3 zu untersuchen, ist die elektronische Konfiguration der Reaktanden von entscheidender Bedeutung. Als Ergebnis erhält man die folgende Regel: sowohl ein stabiles lineares als auch ein zyklisches C6 Molekül können nur gebildet werden, wenn zumindest eines der C3 Moleküle ein teilweise gefülltes Orbital hat, wofür eine Anregung aus dem Singulett-Grundzustand heraus erforderlich ist.