Kurzzeitspektroskopische Untersuchungen der Fotoschutzmechanismen an Lichtsammelkomplexen

In der vorliegenden Arbeit wurden die Photoschutzmechanismen in Pflanzen und Purpurbakterien auf molekularer Ebene experimentell untersucht. Zu diesem Zweck kamen verschiedene spektroskopische Methoden zur Aufklärung der Funktion der dabei vor allem beteiligten Carotinoide zur Anwendung. Die Experimente konzentrierten sich auf die Quenching-Mechanismen von Singulett- und Triplett-Zuständen der elektronisch angeregten (Bacterio-) Chlorophylle. Diese photosynthetischen Reaktionen treten auf ultraschnellen Zeitskalen im Bereich vom Femtosekunden bis Nanosekunden auf, sodass sich Femtosekunden zeitaufgeloeste Absorptionsspektroskopie als geeignetes Methode erweist die molekulare Dynamik in Echtzeit zu verfolgen. Sowohl mittels herkoemmlicher Anreg-Abtast-Spektrokopie als auch mit im Rahmen dieser Arbeit weiter entwickelter resonanter Zwei-Photonen Zwei-Farben Ionisation (R2P2CI), wurden eine Reihe von photosynthetischen Antennensystemen untersucht: Aus photosynthetischen Purpurbakerien wurden der Lichtsammelkomplex 1 (LH1) sowie der Lichtsammelkomplex II (LHC II) und die chlorophyllgebunden Proteine CP24, CP26 und CP29 höherer Pflanzen charakterisiert. Darüber hinaus wurden eine Reihe von Carotinoiden und ihre Radikalkationen als wesentlicher Bestandteil der photoindizierten Reaktionskanaele in Lösung untersucht. Diese Experimente erlauben die Auswirkung der Lösungsmittelpolarität auf die Eigenschaften der Carotinoide (energetische Lage und die Dynamik der angeregten Zustände, Wechselwirkung mit benachbarten photosynthetischen Pigmenten) zu untersuchen.In the present work, the photo-protection mechanisms in plants and purple bacteria were investigated experimentally at the molecular level. For this purpose, several spectroscopic methods were combined and applied to elucidate the function of carotenoids, pigments of the photosynthetic apparatus, in photo-protection. The experiments were focused on the mechanisms involved in quenching of singlet and triplet states of the electronically excited (bacterio)chlorophylls. This photosynthetic reaction events occur on an ultrafast time-scale. Measuring such short-lived events, and understanding the underlying principles, demand some of the most precise experiments and exact measurement technologies currently available. This implies certain requirements for the light source used: a suitable wavelength within the absorption band of the sample, sufficient power, and, most importantly, a pulse duration short compared to the studied reaction. Nowadays, we can achieve all this requirements using femtosecond-spectroscopic systems, which produce laser pulses shorter than 100 femtoseconds (fs). Transient absorption spectroscopy provides important information on molecular dynamics interrogating electronic transitions. The technique is based on photochemical generation of transient species with femtoseconds pump pulses and measuring transient absorption changes of the sample using a second, time delayed probe pulse which in this case is a spectrally broad white-light pulse

Mid-infrared frequency comb spanning an octave based on an Er fiber laser and difference-frequency generation

We describe a coherent mid-infrared continuum source with 700 cm-1 usable bandwidth, readily tuned within 600 - 2500 cm-1 (4 - 17 \mum) and thus covering much of the infrared "fingerprint" molecular vibration region. It is based on nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed Er fiber laser system providing two amplified near-infrared beams, one of them broadened by a nonlinear optical fiber. The resulting collimated mid-infrared continuum beam of 1 mW quasi-cw power represents a coherent infrared frequency comb with zero carrier-envelope phase, containing about 500,000 modes that are exact multiples of the pulse repetition rate of 40 MHz. The beam's diffraction-limited performance enables long-distance spectroscopic probing as well as maximal focusability for classical and ultraresolving near-field microscopies. Applications are foreseen also in studies of transient chemical phenomena even at ultrafast pump-probe scale, and in high-resolution gas spectroscopy for e.g. breath analysis.Comment: 8 pages, 2 figures revised version, added reference

Sub-micron phase coexistence in small-molecule organic thin films revealed by infrared nano-imaging

Controlling the domain size and degree of crystallization in organic films is highly important for electronic applications such as organic photovoltaics, but suitable nanoscale mapping is very difficult. Here we apply infrared-spectroscopic nano-imaging to directly determine the local crystallinity of organic thin films with 20-nm resolution. We find that state-of-the-art pentacene films (grown on SiO2 at elevated temperature) are structurally not homogeneous but exhibit two interpenetrating phases at sub-micrometre scale, documented by a shifted vibrational resonance. We observe bulk-phase nucleation of distinct ellipsoidal shape within the dominant pentacene thin-film phase and also further growth during storage. A faint topographical contrast as well as X-ray analysis corroborates our interpretation. As bulk-phase nucleation obstructs carrier percolation paths within the thin-film phase, hitherto uncontrolled structural inhomogeneity might have caused conflicting reports about pentacene carrier mobility. Infrared-spectroscopic nano-imaging of nanoscale polymorphism should have many applications ranging from organic nanocomposites to geologic minerals

Nanomechanical behavior of polystyrene/graphene oxide nanocomposites

The in-situ investigation of the nanomechanical features of the polymer graphene nanocomposites has become a challenging and an indispensable task to achieve the required application. Graphene oxide (GO) nanocomposites were prepared at 1.0% weight fraction of GO to reinforce polystyrene (PS) using solution blending approach. The morphology of the resulting nanocomposites was characterized by optical, scanning electron, transmission electron, atomic force, and scattering scanning near-field optical microscopies. These showed a uniform dispersion of graphene oxide nano-sheets in the PS matrix. By adopting Derjaguin–Muller–Toporov (DMT) formula, the nanomechanical properties for the cryogenically fractured surface of the composites were characterized using the traditional atomic force microscopy (AFM), peak-force quantitative nanomechanical mapping (QNM), and tip-force mode functioned with scattering scanning near–field optical microscopy (s-SNOM). Young’s modulus of the PS matrix varied around (1–2) GPa as shown by QNM and s-SNOM similar to what was reported in the literature. However, while putative GO nano-sheets were measured to have a higher elastic modulus than the surrounding matrix in Peak-Force QNM experiments, they were significantly below literature values. By using Tip-Force mode related to s-SNOM, the expected values of Young’s modulus for GO were recovered

Nanomechanical behavior of polystyrene/graphene oxide nanocomposites

The in-situ investigation of the nanomechanical features of the polymer graphene nanocomposites has become a challenging and an indispensable task to achieve the required application. Graphene oxide (GO) nanocomposites were prepared at 1.0 weight fraction of GO to reinforce polystyrene (PS) using solution blending approach. The morphology of the resulting nanocomposites was characterized by optical, scanning electron, transmission electron, atomic force, and scattering scanning near-field optical microscopies. These showed a uniform dispersion of graphene oxide nano-sheets in the PS matrix. By adopting Derjaguin–Muller–Toporov (DMT) formula, the nanomechanical properties for the cryogenically fractured surface of the composites were characterized using the traditional atomic force microscopy (AFM), peak-force quantitative nanomechanical mapping (QNM), and tip-force mode functioned with scattering scanning near–field optical microscopy (s-SNOM). Young’s modulus of the PS matrix varied around (1–2) GPa as shown by QNM and s-SNOM similar to what was reported in the literature. However, while putative GO nano-sheets were measured to have a higher elastic modulus than the surrounding matrix in Peak-Force QNM experiments, they were significantly below literature values. By using Tip-Force mode related to s-SNOM, the expected values of Young’s modulus for GO were recovered

Primary signet ring cell carcinoma of gall bladder: report of an extremely rare histological type of primary gall bladder carcinoma

Signet ring cell carcinoma is an extremely rare type of gall bladder carcinoma composed overwhelmingly (90%) of signet ring cells. It is necessary to exclude a gastric or colonic signet ring cell carcinoma secondarily involving the gall bladder. The primary aim of this case report is to describe the histopathological aspects of this tumour. Primary signet ring cell carcinoma of gall bladder shows dysplastic surface gall bladder epithelium with infiltration of gall bladder wall. It is also necessary to exclude benign signet ring change, which sometimes occurs in the gall bladder. However, it is always confined to the mucosa and does not infiltrate the wall. This case showed grossly diffuse thickening of the gall bladder wall and dysplastic surface epithelium of the gall bladder on histology, with sheets of signet ring cells infiltrating full thickness of the wall. It is also necessary to exclude benign signet ring cell change, which sometimes occurs in the gall bladder. However it is always confined to the mucosa and does not infiltrate the wall

Nano-FTIR Absorption Spectroscopy of Molecular Fingerprints at 20 nm Spatial Resolution

We demonstrate Fourier transform infrared nanospectroscopy (nano-FTIR) based on a scattering-type scanning near-field optical microscope (s-SNOM) equipped with a coherent-continuum infrared light source. We show that the method can straightforwardly determine the infrared absorption spectrum of organic samples with a spatial resolution of 20 nm, corresponding to a probed volume as small as 10 zeptoliter (10^–20 L). Corroborated by theory, the nano-FTIR absorption spectra correlate well with conventional FTIR absorption spectra, as experimentally demonstrated with poly­(methyl methacrylate) (PMMA) samples. Nano-FTIR can thus make use of standard infrared databases of molecular vibrations to identify organic materials in ultrasmall quantities and at ultrahigh spatial resolution. As an application example we demonstrate the identification of a nanoscale PDMS contamination on a PMMA sample