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Die Zellmembran dient der Zelle nicht nur als äußere Hülle, sondern ist auch an einer Vielzahl von lebenswichtigen Prozessen wie Signaltransduktion oder Zelladhäsion beteiligt. Wasser als integraler Bestandteil von Zellen und der extrazellulären Matrix hat sowohl einen großen Einfluss auf die Struktur von Biomolekülen, als auch selbst besondere Merkmale in eingschränkter Geometrie. Im Rahmen dieser Arbeit wurden zwei Effekte an Modellmembranen untersucht: Erstens der Einfluss des Gegenions an kationischen Lipiden (DODAX, X = F, Cl, Br, I) auf die Eigenschaften des Grenzflächenwassers und zweitens das Vermögen durch Viskositätsänderungen das Wachstum von Nervenzellen anzuregen sowie die einzelnen Stadien der Bildung von neuronalen Netzwerken und deren Optimierung zu charakterisieren. Lipidmultischichten und darin adsorbiertes Grenzflächenwasser wurden mittels Infrarotspektroskopie mit abgeschwächter Totalreflexion untersucht. Nach Charakterisierung von Phasenverhalten und Wasserkapazität der Lipide wurden die Eigenschaften des Wassers durch kontrollierte Hydratisierung bei einem Wassergehalt von einem Wassermolekül pro Lipid verglichen. Durch die geringe Wasserkapazität können in diesem besonderen System direkte Wechselwirkungen zwischen Lipiden und Wasser aus der ersten Hydratationsschale beobachtet werden. Bemerkenswert strukturierte OH-Streckschwingungsbanden in Abhängigkeit des Anions und niedrige IR-Ordnungsparameter zeigen, dass stark geordnete, in ihrer Mobilität eingeschränkte Wassermoleküle an DODAX in verschiedenen Populationen mit unterschiedlich starken Wasserstoffbrückenbindungen existieren und sich vermutlich in kleinen Clustern anordnen. Die zweite Fragestellung hatte zum Ziel, das Wachstum von Nervenzellen auf Membranen zu beleuchten. Auf der Ebene einzelner Zellen wurde untersucht, ob sich in Analogie zu den bisher verwendeten elastischen Substraten, die Viskosität von Membranen als neuartiger physikalischer Stimulus dafür eignet, das mechanosensitive Verhalten von Neuronen zu modulieren. Das Wachstum der Neuronen wurde auf substrat- und polymergestützten Lipiddoppelschichten mittels Phasenkontrastmikroskopie beobachtet. Die Quantifizierung der Neuritenlängen, -auswuchsgeschwindigkeiten und -verzweigungen zeigten kaum signifikante Unterschiede. Diffusionsmessungen (FRAP) ergaben, dass entgegen der Erwartungen, die Substrate sehr ähnliche Fluiditäten aufweisen. Die Betrachtung der zeitlichen Entwicklung des kollektiven Neuronenwachstums, also der Bildung von komplexen Netzwerken, offenbarte robuste „Kleine-Welt“-Eigenschaften und darüber hinaus unterschiedliche Stadien. Diese wurden durch graphentheoretische Analyse beschrieben, um anhand typischer Größen wie dem Clusterkoeffizienten und der kürzesten Pfadlänge zu zeigen, wie sich die Neuronen in einem frühen Stadium vernetzen, im Verlauf eine maximale Komplexität erreichen und letztlich das Netzwerk durch effiziente Umstrukturierung hinsichtlich kurzer Pfadlängen optimiert wird.

Fourier transform infrared difference spectroscopy (FTIR DS) is widely used to study the structural details of electron transfer cofactors in photosynthetic protein complexes. In photosynthetic proteins quinones play an important role, functioning as a cofactor in light-driven electron transfer. In photosystem I (PS I) phylloquinone (PhQ) functions as an intermediary in electron transfer. To investigate the properties of PhQ that occupies the, so called, A1 binding site in PS I, time-resolved step-scan FTIR DS, with 5µs time resolution at 77K has been used. By replacing PhQ in the A1 binding site with specifically isotope labeled version, information on the vibrational frequencies associated specifically with the quinone in the binding site were obtained, which could be compared to the vibrational properties of quinone in solution or quinones in other protein binding sites. To further aid in assessing the origin of bands in the spectra, quantum mechanics /molecular mechanics (QM/MM) ONIOM type calculations were undertaken. ONIOM is an acronym for Our own N-layered Integrated molecular Orbital and molecular Mechanics. We find that the phytyl tail of PhQ does not play an important role in the orientation of PhQ in the A1 binding site. We also find that PhQ, in both neutral and reduced states, is strongly hydrogen bonded. To test and verify the applicability of our QM/MM approach, ONIOM calculations were also undertaken for ubiquinone and a variety of other quinones incorporated into the, so called, QA binding site in purple bacteria photosynthetic reaction centers. The calculated and experimental spectra agree well, demonstrating the utility and applicability of our ONIOM approach. Hydrogen bonding to the carbonyl groups of quinones in the QA binding site was shown to be relatively weak, and it was found that hydrogen bonding to neutral ubiquinone in purple bacterial reaction centers can be considered in purely electrostatic terms, contrary to the widely held belief that the hydrogen bonding amino acids should be treated quantum mechanically.

In recent years bleaching of vital teeth has become popular among both dentist and patients. Different bleaching agents were used for this purpose. They are either applied professionally at high dose (office bleaching) or by patient at lower dose (home bleaching). In the present work we studied the effects of a high concentration bleaching agent (35% hydrogen peroxide), and a low concentration bleaching agent (17% carbamide peroxide) on human enamel and dentin using Fourier Transform Infrared (FTIR) Spectroscopic Technique. The OH stretching band of hydroxyapatite at 3567 cm-1 appeared in the spectra of enamel tissue which was absent in dentin. Carbamide peroxide and hydrogen peroxide treatment induced some differences in enamel and dentin spectra according to control group spectra. While the treatment of hydrogen peroxide leaded to significant decrease in mineral to matrix ratio, carbamide peroxide treatment did not cause decrease in this level. In addition, organic components of the teeth were changed after the treatment of bleaching agents. The frequency of the Amide A and Amide I bands were significantly changed for enamel tissue after the treatment of high concentration bleaching agent. However, it is observed that these changes result from two different bleaching methods are negligible in dentin tissue. In conclusion it can be stated that hydrogen peroxide treatment caused dramatic changes in enamel structure according to carbamide peroxide treatment, but two methods did not cause significant changes in dentin tissue.

Les biosenseurs sont des dispositifs analytiques utilisés pour la détection de reconnaissance moléculaire. Ils consistent en un élément biologique immobilisé en contact intime avec un transducteur approprié qui convertit un signal biochimique en un signal électrique quantifiable. Leur principe est basé sur la reconnaissance d'une ou plusieurs molécules d'intérêt en solution (le ligand), par un composant biologique (le récepteur) étroitement lié au substrat transducteur. Le senseur réagit aux interactions récepteur-ligand et produit un signal mesurable, généralement proportionnel à la concentration du ligand fixé. Les biosenseurs sont déjà utilisés dans beaucoup de domaines différents, notamment dans le domaine médical (diagnostique et thérapeutique), le contrôle de l’environnement, et l’analyse et le monitoring de processus biotechnologiques. <p><p>La recherche concerne la mise au point d’un nouveau type de biosenseurs polyvalents à haute performance. Ces senseurs utilisent un élément de transduction optique dont la surface a été fonctionnalisée en vue de permettre la détection sélective d'interactions récepteur-ligand ainsi que le dosage des molécules fixées aux récepteurs. La technique utilisée pour la détection et le dosage est celle de la Spectroscopie ATR-FTIR (Spectroscopie Infra Rouge à Transformée de Fourrier en Réflexion Total Atténuée). Le système permet la détection directe, en temps réel, et sans marquage des molécules ciblées. La spectroscopie ATR-FTIR fournit une analyse des molécules sur base de leur empreinte spectrale infra rouge (IR) caractéristique, ce qui offre une mine d'informations pour identifier les ligands. Ce nouveau système de biosenseur, appelé BIA-ATR (Biospecific Interaction Analysis – Attenuated Total Reflection) est original et offre des avantages majeurs par rapport à la plus part des biosenseurs commercialement disponibles. Il fournit à l’utilisateur le spectre IR entier du ligand étudié, permettant non seulement le dosage quantitatif de ce dernier, mais aussi d’identifier sa nature intrinsèque. Un autre avantage est sa grande sensibilité ;le senseur BIA-ATR peut détecter la fixation de petites molécules et dans certains cas, aussi les réactions chimiques associées. <p><p>Le potentiel de cette nouvelle technologie de senseur est évalué dans ce travail par son application à plusieurs systèmes d’intérêt biologique et médical :la détection de protéines en milieux complexes, appliquée à la détection du Facteur VIII de coagulation du sang impliqué dans l’hémophilie de type A ;la fixation d’une petite molécule, le phosphate (phosphorylation), sur l’ATPase gastrique, un récepteur protéique de grande taille responsable de la sécrétion d’acide dans l’estomac et la détection et dosage d’un antibiotique, la vancomycine, utilisé en soins intensifs hospitaliers dans les cas d’infections bactériennes sévères à Staphylocoques dorés.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Orientadores: Florencia Cecilia Menegalli, Paulo Jose do Amaral Sobral / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-10T03:02:54Z (GMT). No. of bitstreams: 1 AraujoFarro_PatriciaCecilia_D.pdf: 11234576 bytes, checksum: 783552b6dbe46ec622ef24d255cee671 (MD5) Previous issue date: 2008 / Resumo: O grão de quinoa (Chenopodium quinoa, Willdenow) é um pseudocereal originário da América do Sul Andina, que tem gerado interesse industrial crescente e cultivo diversificado em diversos países de América do Norte e da Europa. Recentemente nos países da América Latina tem-se despertado um interesse comum na busca de tecnologias de desenvolvimento de biomateriais, como uma forma de diminuir a poluição gerada pelos resíduos sintéticos, utilizando os recursos naturais próprios da região. O Brasil destaca-se pela sua preocupação pelo meio ambiente e manutenção das fontes destes recursos, através de programas experimentais de adaptação de culturas, como a quinoa, nos cerrados brasileiros, com resultados satisfatórios. O uso potencial da quinoa na indústria alimentícia tem sido alvo de estudos diversos. No entanto, é pouco explorada a aplicabilidade de produtos derivados deste grão, como farinhas e amido, na área de biomateriais. Dentro desse contexto, os principais objetivos deste trabalho foram: (1) desenvolver tecnologias pouco agressivas de extração de matérias-primas a partir do grão de quinoa: farinha integral (FI); farinha por extração úmida (FU) e amido (AQ); (2) caracterização das propriedades físico-químicas e estruturais destes produtos; (3) análises reológicas de soluções formadoras de filmes a partir do amido; (4) avaliação de diferentes formulações utilizadas na elaboração de filmes utilizando um planejamento fatorial completo analisando os efeitos de concentração de glicerol, do pH da solução filmogênica, e das condições de secagem (T(ºC) / t (horas)) em função da solubilidade e das propriedades mecânicas dos filmes; (5) otimização do processo de elaboração de filmes e caracterização dos filmes ótimos quanto às propriedades termomecânicas, óticas e estruturais, e cristalinidade (FTIR e Raios X). Os filmes elaborados a partir das diferentes matérias-primas obtidas do grão de quinoa foram elaborados utilizando 4% de matéria prima/ 100 g de solução filmogênica. Esta porcentagem da matéria prima foi determinada através das análises reológicas. Foi utilizado um planejamento fatorial completo 23, onde as três variáveis independentes foram: concentração de glicerol (16,6; 20; 25; 30 e 33,4 g/100 g matéria-prima), nível de pH de soluções filmogênica (9,7; 10; 10,5; 11 e 11,3) e condições de secagem (30°C/20h; 34°C/17h; 40°C/10h; 46°C/9h e 50°C/5h). As variáveis respostas foram: teste mecânico de tração (força na tração e elongação no ponto de ruptura); teste mecânico de perfuração (força na perfuração e deformação na perfuração) e solubilidade em água a 25ºC. Uma vez determinadas as equações dos modelos matemáticos, foi aplicada a função desejabilidade para estabelecer as condições ótimas de elaboração de filmes. Para o filme de amido de quinoa, a condição ótima foi obtida com concentração de glicerol de 21,2%, pH de 10,7 e condição de secagem de 36ºC/14h. Para o filme de FU: Concentração de glicerol de 21%, nível de pH de 10,48 e condição de secagem de 42ºC/8h. E para o filme de FI foi de concentração de glicerol de 20%, nível de pH de 10,6 e condição de secagem de 38ºC/12h. Os filmes de amido de quinoa mostraram-se incolores e pouco opacos, apresentando reduzida solubilidade em água e boa resistência à tração e flexibilidade. Os filmes de farinha por extração úmida apresentaram leve cor amarela, moderada opacidade e flexibilidade. Já os filmes de farinha integral apresentaram cor amarela intensa, moderada opacidade, alta flexibilidade mas baixa resistência no teste de tração / Abstract: Quinoa (Chenopodium quinoa, Willdenow) is a native and oldest pseudocereal grain from the Andean region in South America. Nowadays, due to an increasing industrial interest, quinoa seeds are grown in different countries as in North America and Europe. Recently, Latin American countries have shared a common interest regarding the use of natural resources in technologies capable of minimizing pollution. In that sense, special attention has been given towards the development of new biomaterials that could diminish synthetic residues. In the last years, Brazil participated in experimental programs of culture adaptation, with satisfactory results for quinoa crops. In spite of the great amount of studies concerning the potential use of quinoa in the food industry, the use of the quinoa seeds as source of starch and flour and their applicability in the biomaterials development field has not yet been fully explored. The aims of this work were: (1) to develop a non aggressive raw material (starch and flours) extraction technique, (2) determine the structural and physical-chemical properties of the quinoa products (3) characterization of the film-forming solutions through rheological analyses (4) to evaluate the effects of the glycerol content, pH and drying conditions of film-forming solutions on some functional properties of its edible films using an experimental design (response surface methodology). The responses were mechanical properties as puncture strength, puncture deformation, tensile strength, elongation and Young modulus and solubility, (5) optimization of the films elaborative process and characterization (thermomechanical, optical and structural properties, and crystallinity - FTIR and X-ray) of the optimal quinoa films. According to an experimental design 23, films were produced from film forming solutions (FFS) containing 4g of Quinoa products (QP) /100g of FFS (this percentage of QP was determined by rheological tests), glycerol (16.6, 20.0, 25.0, 30.0 and 33.4 g/100 g starch) used as a plasticizer, and a constant pH of FFS (9.7, 10.0, 10.5, 11.0 and 11.3). Drying conditions varied from temperature and time (30°C/20h; 34°C/17h; 40°C/10h; 46°C/9h and 50°C/5h) in an oven with circulation and renewal of air. The five levels of each variable were coded as -1.68, - 1, 0, +1, +1.68. All tests were run at room conditions (22-25ºC and 55-65% relative humidity) using samples previously conditioned at 58% of relative humidity at 22-25ºC for 7 days. The optimal films elaboration conditions were determined by the desirability function. For each quinoa product, conditions were different. For films based on starch (S), the optimal condition was obtained when using 21,2% glycerol content, pH= 10,7 and drying condition of 36ºC/14h, for films of flour extracted by wet milling (FWM), 21% glycerol content, pH= 10,48 and drying condition of 42ºC/8h, and, finally, for films of whole flour (WF), 20% glycerol content, pH= 10,6 and drying condition of 38ºC/12h The S films were colorless and scarcely opaque, showed reduced water solubility, and presented good qualities of tensile strength. FWM films presented a yellowish color, moderate opacity, tensile strength and flexibility. WF films presented an intense yellowish color, moderate opacity and high flexibility but low tensile strength / Doutorado / Doutor em Engenharia de Alimentos

Les effets de différentes activités anthropiques (vignoble, cuverie) sur les populations fongiques du raisin au vin ont été étudiés. Afin de caractériser ces effets, il était nécessaire d’avoir accès à la diversité globale des populations (pyroséquençage et IR-TF) mais également à la diversité intraspécifique (IR-TF). La spectroscopie a ainsi été validée pour sa capacité à caractériser la population globale et à discriminer les souches pour trois espèces de levures non-Saccharomyces (NS). Pour la première fois, il est démontré que la baie de raisin constitue une source limitée pour les levures NS alors que la cuverie semble constituer une source importante; l’air étant un vecteur important de dissémination de ces levures. De plus, la persistance et la réimplantation des levures NS dans le moût l’année suivante ont été démontrées. Les activités anthropiques étudiées modifient la diversité fongique. Une biodiversité plus faible pour les raisins de la modalité biologique a été mesurée pour les 3 millésimes considérés. Les populations fongiques sont ensuite fortement remaniées par l’étape de pressurage/clarification et l’influence de la flore de cuverie est confirmée. L’ajout de SO2 modifie les dynamiques des populations et favorise la domination de l’espèce S. cerevisiae. L’analyse chimique non-ciblée des vins montre pour la première fois que ces derniers peuvent être discriminés à la fin de la fermentation alcoolique en fonction de la protection phytosanitaire, que ces fermentations aient eu lieu en présence ou non de SO2. Ainsi, l'existence dans les vins de signatures de diversité chimique et microbiologique liées au mode de protection au vignoble est mise en évidence. / The effects of different anthropogenic activities (vineyard, winery) on fungal populations from grape to wine were studied. To characterize these effects, it was necessary to access to the overall diversity of populations (pyrosequencing and spectroscopy FT-IR) but also to intra-specific diversity (FT-IR). Spectroscopy FT-IR has been validated for their ability to characterize the global population and to discriminate the strains for three species of non-Saccharomyces yeasts (NS). For the first time, it is shown that the grape berry is a limited source for NS yeasts while the winery seems to be a significant source; the air is an important vector for dissemination of these yeasts. In addition, persistence of NS yeast strains from year to year in the winery has been demonstrated. The studied anthropogenic activities modify the fungal diversity. Thus, lower biodiversity of grapes from organic modality was measured for the three vintages considered. The pressing / clarification step revises strongly fungal populations and the influence of the winery flora is confirmed. The addition of SO2 changes the population dynamics and favors the dominance of the species S. cerevisiae. The non-targeted chemical analysis shows, for the first time, that these wines can be distinguished at the end of the alcoholic fermentation (with or without SO2) depending on plant protection. Thus, the existence in wines of chemical and microbiological signatures associated with vineyard protection mode is highlighted.

La lipase pancréatique apparentée de type 2 du cobaye (GPLRP2) hydrolyse une grande variété de substrats lipidiques. Elle montre cependant une sélectivité selon l’organisation supramoléculaire du substrat et la présence de surfactants comme les sels biliaires (NaTDC). Nous avons utilisé la spectroscopie infrarouge (FTIR) pour étudier les interactions entres les phospholipides (DPPC), les surfactants et la GPLRP2 dans des conditions expérimentales proches de celles du tractus digestif. Pour étudier l’étape d’adsorption indépendamment de l’hydrolyse, un variant inactif de GPLRP2 (S152G) a été produit. Diverses dispersions aqueuses de phospholipides ont été préparées : des vésicules multilamellaires (MLV), unilamellaires (LUV) et des micelles mixtes DPPC-surfactant. GPLRP2 hydrolyse le DPPC présent dans des micelles mixtes DPPC-NaTDC mais n’a aucune activité sur le DPPC en phase lamellaire ou présent dans des micelles DPPC-Triton X100. L’analyse par FTIR de l’interaction de GPLRP2 S152G avec le système DPPC-NaTDC montre des changements importants dans le désordre conformationnel et la mobilité des chaînes acyles, la déshydratation de l’interface, l’orientation des têtes polaires et leurs liaisons hydrogène. Aucun effet n’est observé avec les MLV, les LUV ou le système DPPC-Triton X100. Il y a ainsi une reconnaissance spécifique du DPPC dans les micelles mixtes avec les sels biliaires, en accord avec l’activité enzymatique de GPLRP2. Les changements du spectre IR pendant l’hydrolyse du DPPC par la GPLRP2 ont été suivis. Certaines caractéristiques attribuées à la formation de produits de lipolyse peuvent être utilisées pour une étude quantitative de la lipolyse par FTIR. / Guinea pig pancreatic lipase-related protein type 2 (GPLRP2) hydrolyzes a large set of lipid substrates, but displays however some selectivity depending on the supramolecular structure of substrate and the presence of surfactants like bile salts (NaTDC). We used Fourier transform infrared (FTIR) spectroscopy to study the interactions between phospholipids (DPPC), surfactants and GPLRP2 under conditions close to those of the GI tract. To study the adsorption step independently from hydrolysis, a GPLRP2 inactive variant (S152G) was produced. Various phospholipid dispersions were prepared: multilamellar (MLV) and large unilamellar vesicles (LUV) and mixed micelles with surfactants. GPLRP2 was found to hydrolyze DPPC present in mixed DPPC-NaTDC micelles but was inactive on DPPC vesicles and DPPC-Triton X100 micelles. FTIR analysis of GPLRP2 S152G interaction with the DPPC-NaTDC system showed a decrease in the conformational disorder and mobility of the acyl chains, a dehydratation of the interface, and changes in the orientation and H-bonding of DPPC polar head-groups. These effects were not observed with MLV, LUV and DPPC-Triton X100 micelles, thus indicating a specific recognition of DPPC in mixed phospholipid-bile salt micelles, in agreement with phospholipase activity measurements. Changes in the IR spectra during DPPC hydrolysis by GPLRP2 were monitored. Specific spectral features were associated to the production of lipolysis products and could be used for quantifying phospholipid lipolysis by FTIR.

The feasibility of FTIR-based spectroscopy as a tool to measure cellular response to therapeutics was investigated. Fourier transform mid-infrared spectroscopy has been used in conjunction with multivariate analysis (MVA) to assess the chemistry of many clinically relevant biological materials; however, the technique has not yet found its place in a clinical setting. One issue that has held the technique back is due to the spectral distortions caused by resonant Mie scattering (RMieS), which affects the ability to confidently assign molecular assignments to the spectral signals from biomaterials. In the light of recently improved understanding of RMieS, resulting in a novel correction algorithm, the analytical robustness of corrected FTIR spectra was validated against multi-discipline methods to characterise a set of renal cell lines which were selected for their difference in morphology.After validation of the FTIR methodology by discriminating different cell lines, the second stage of analyses tested the sensitivity of FTIR technique by determining if discrete chemical differences could be highlighted within a cell population of the same origin. The renal carcinoma cell line 2245R contains a sub-population to contain a sub-population of cells displaying 'stem-cell like' properties. These stem-like cells, however, are difficult to isolate and characterise by conventional '-omic' means. Finally, cellular response to chemotherapeutics was investigated using the established renal cell lines CAKI-2 and A-498. For the model, 5-fluorouracil (5FU), an established chemotherapeutic agent with known mechanisms of action was used. Novel gold-based therapeutic compounds were also assessed in parallel to determine their efficacy against renal cell carcinoma. The novel compounds displayed initial activity, as the FTIR evidence suggested compounds were able to enter the cells in the first instance, evoking a cellular response. The long-term performance, tracked with standard proliferation assays and FTIR spectroscopy in the renal cancer cell model, however, was poor. Rather than dismissing the compounds as in-active, the compounds may simply be more effective in cancer cell types of a different nature. The FTIR-based evidence provided the means to suggest such a conclusion. Overall, the initial results suggest that the combination of FTIR and MVA, in the presence of the novel RMieS-EMSC algorithm can detect differences in cellular response to chemotherapeutics. The results were also in-line with complimentary biological-based techniques, demonstrating the powerful potential of the technique as a promising drug screening tool.

Kanalrhodopsine (ChRs) sind lichtgesteuerte Ionenkanäle aus einzelligen Grünalgen, die in der Optogenetik verwendet werden. Photonabsorption führt zur Isomerisierung des Retinal-Kofaktors, was eine Reihe von Reaktionen auslöst, die als Photozyklus bezeichnet werden und die Bildung des leitenden Zustands umfassen. In dieser Arbeit wurde der Photozyklus-Mechanismus ausgewählter ChRs mittels FTIR (Fourier Transform Infrarot)- und UV-Vis-Spektroskopie, sowie Retinalextraktion und HPLC (Hochleistungsflüssigkeitschromatographie)-Analyse untersucht. Photorezeptoren sind dafür optimiert, Lichtenergie zu nutzen, um Konformationsänderungen des Proteins hervorzurufen. Dafür wird ein Teil der Lichtenergie durch eine transiente Verdrillung des Chromophors gespeichert. In dieser Arbeit wird gezeigt, dass der Transfer der gespeicherten Energie zum Protein in ReaChR stark vom Protonierungszustand von Glu163 beeinflusst wird; er wird durch eine erhöhte Rigidität des aktiven Zentrums bei protoniertem Glu163 verlangsamt. In Chrimson hingegen relaxiert der Chromophor nach Photoisomerisierung, was auf einen verdrillten Chromophor im Dunkelzustand hinweist, was vermutlich für die bathochrome Verschiebung von Bedeutung ist. Zusätzlich zur Chromophorgeometrie beeinflusst der Protonierungszustand von Glu163 in ReaChR und dem homologen Glu165 in Chrimson die Stereoselektivität der Photoreaktion. Ein weiterer Faktor der Stereoselektivität ist Asp196 in ReaChR (Asp195 in C1C2), welches im Photozyklus deprotoniert. Die Bildung des leitenden Zustands in C1C2 und ReaChR geht mit einem Wassereinstrom ins Protein einher, welcher den Transport größerer Kationen erleichtert. Die Deprotonierung von Glu130 in ReaChR (Glu129 in C1C2) verändert die Ionenselektivität des Kanals, wie aus elektrophysiologischen Messungen bekannt ist. In Chrimson ist das Ausmaß des Wassereinstroms deutlich reduziert, was – in Übereinstimmung mit elektrophysiologischen Experimenten – den Transport von Protonen begünstigt. / Channelrhodopsins (ChRs) are light-gated ion channels found in single-cell algae and used in optogenetics. Photon absorption leads to isomerization of the retinal cofactor, initiating a number of reactions that are referred to as photocycle and involve formation of the ion-conducting state. In this thesis, the photocycle mechanism of selected ChRs was investigated using FTIR (Fourier Transform Infrared) and UV-Vis spectroscopy, as well as retinal extraction and subsequent HPLC (High Performance Liquid Chromatography) analysis. Photoreceptors are optimized to use photon energy to drive conformational changes of the protein. Therefore, a fraction of the photon energy is stored by a transient distortion of the chromophore. In this thesis, it is shown that in ReaChR the transfer of the stored energy to the protein is largely affected by the protonation state of Glu163, being decelerated by protonated Glu163 due to an enhanced rigidity of the active site. In contrast, the chromophore in Chrimson relaxes upon photoisomerization, hinting at a distorted retinal geometry in the dark state, which is probably essential for its unprecedented bathochromic absorption. In addition to the chromophore geometry, the protonation state of Glu163 in ReaChR and the homologue Glu165 in Chrimson affects the stereoselectivity of the photoreaction. Another factor for stereoselectivity is Asp196 in ReaChR (Asp195 in C1C2) which deprotonates in the photocycle. Formation of the ion-conducting state in C1C2 and ReaChR involves water influx into the protein, facilitating transport of larger cations. Deprotonation of Glu130 in ReaChR (Glu129 in C1C2) alters the ion selectivity of the channel as known from electrophysiological experiments. In Chrimson, the extent of water influx is drastically reduced which favors the conductance of protons in agreement with electrophysiological characterization.