09:00
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R. Herges
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Welcome
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show abstract
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09:20
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S. Boretius
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project proposal
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show abstract
Magnetic resonance imaging (MRI) is a noninvasive 3D imaging technique used with increasing frequency in biomedical research and in medical diagnostics of animals and humans. Besides temporally and spatially highly resolved anatomical information, MRI can yield insights into metabolism and function of an intact living organism. However, although MRI provides an excellent native tissue contrast even from volumes localized deeply insides the body, the specificity of contrast alterations for different physico-chemical properties of the structures is limited. A brief overview of current possibilities will also highlight one other limitation, namely limited sensitivity of current in vivo MR imaging and spectroscopy.
Fig. 1: Signal intensity on T1- weighted images of a “record player- molecule” before and under irradiation with green and violet light, respectively
MRI contrast agents that can switch their magnetic properties depending on the physical and chemical environment are of great interest in this context. The possibility to change the specific relaxivity in a rapidly reversible manner may provide new opportunities for quantitative molecular imaging approaches. Different molecules, magnetic properties of which can be changed by light irradiation, were analyzed using specifically adapted MRI methods. Here we present first preliminary results demonstrating changes in magnetic resonance properties of molecules with porphyrine-based chemical structures synthesized in the group of R. Herges. A number of analogues have been tested and of particular interest in biomedical research may be our observation that not only the specific record-player molecules introduced in Fig. 1 but also hemoglobin irritated by light (405-528 nm) can induce reversible contrast alteration on T1-weighted images; further experiments have to be designed to fully understand the nature of these changes. Concerning application in biomedical research and medical diagnostics switching by visible light has the disadvantage of low tissue penetration depth, however there may be interesting new applications in flow measurements, localization of instruments in the human body during medical interventions or in the analysis of biological processes on surfaces.
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09:50
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B. Hartke
A05
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progress report
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show abstract
Project A5 aims at quantitative single-molecule measurements of optomechanical molecular switches, joining organic synthesis, conducting-AFM measurements and theory. Correspondingly, we report on recent progresses in synthesizing suitable molecular systems, in detecting length and conductance changes, and in theoretical modeling of these processes.
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10:10
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P. Ferriani
B10
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progress report
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show abstract
In this project, we use first-principles electronic structure calculations based on density functional theory to investigate the structural, electronic, and magnetic properties of molecules on surfaces. Here, a short overview of the current research activities in the project and the future perspective will be given. In the past two years, we have worked on four different topics: (i) We have studied the role of graphene in mediating the magnetic interaction between a molecular spin and magnetic substrates [1]. In particular, we have demonstrated sizable exchange coupling between cobaltocene (CoCp2) adsorbed on graphene deposited on Ni(111) and show how intercalation by magnetic monolayers of Fe or Co allows to tune the interaction between ferro- and antiferromagnetic coupling. (ii) We show that the magnetic properties of a two-dimensional transition-metal antiferromagnet are modified on the atomic scale by the adsorption of small organic molecules [2]. (iii) We study the interaction between individual molecules on surfaces and scanning probe microscope tips. We calculate the distant-dependent force and conductance between a Ag tip and a Sn-Pc molecule adsorbed on Ag(111). These investigations are linked to experimental work in the group of R. Berndt. (iv) We investigate magnetic shuttlecock molecules such as M-Pc on graphene on Ni(111). We predict for the case of NbPc both configurations with the Nb atom above or below the Pc plane to be stable and separated by an energy barrier. Our results suggest that switching between them would be achievable by applying voltage pulses in spin-polarized STM experiments and it would results in switching on and off the magnetic moment of the molecule.
[1] S. Marocchi, P. Ferriani, N. M. Caffrey, F. Manghi, S. Heinze, and V. Bellini, “Graphene-mediated exchange coupling between a molecular spin and magnetic substrates”, submitted to Nano Letters.
[2] Nuala M. Caffrey, Paolo Ferriani, Simone Marocchi, and Stefan Heinze, “Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface”, submitted to Phys. Rev. B.
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10:30
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R. Adelung
C10
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progress report
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show abstract
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10:50
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coffee break
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11:10
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F. Tuczek
A03
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progress report
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show abstract
Spin state switching in homogeneous solution and on surfaces: Experimental and theoretical results
The switching behaviour of Fe(II) and Fe(III) complexes coordinated by photoswitchable phenylazopyridine ligands has been investigated, and the consequences of the trans cis photoisomerization of the coordinated ligands with respect to the magnetic properties of the central ion have been determined. The experimental data are compared with DFT calculations of the complexes in their high spin and low spin states, respectively.[1] The results obtained on iron complexes are compared with data obtained on Ni(II) porphyrin complexes coordinated with analogous ligands,[2-5] in which a change in the coordination number is employed to change the spin state of the central ion (CISSS and LD-CISSS, respectively). The Fe and Ni complexes have also been attached to surfaces and investigated with IRRAS, XPS, NEXAFS, and STM.[6] In addition, thin films of the iron complexes [FeII(H2Bpz)2(phen)] and [FeII(H2Bpz)2(bipy)] have been prepared by vacuum deposition and investigated with respect to their spin crossover behaviour (H2Bpz = bis(pyrazolyl)borate).[7] For the first time light-induced excited spin state trapping (LIESST) has been observed in such systems. T1/2 and TLIESST in the films have been found to be in agreement with the bulk values. In double layers of these complexes on Au(111) spin-state switching on the single-molecule level has been observed.[8-10]
Funding of this research by DFG (SFB 677) is gratefully acknowledged.
[1] A. Bannwarth, S.-O. Schmidt, G. Peters, W. Thimm, R. Herges, F. Tuczek . Eur. J. Inorg. Chem. 2012, 2776
[2] S. Thies, C. Bornholdt, F. Köhler, F. D. Sönnichsen, C. Näther, F.Tuczek, R. Herges Chem. Eur. J. 2010, 16, 9928
[3] S. Venkataramani, U. Jana, M.Dommaschk, F. D. Sönnichsen, F.Tuczek, R. Herges Science 2011, 331, 445
[4] S. Thies, C. Bornholdt, C. Näther, F. Tuczek, R. Herges J.Am.Chem.Soc. 2011, 133, 16243
[5] S. Thies, H. Sell, C. Bornholdt, C. Schütt, F. Köhler, F. Tuczek R. Herges Chem. Europ. J. 2012, 18, 16358
[6] H.Jakob, K. Kathirvel, F.Petersen, A. Bannwarth, S.-O. Schmidt, S. Meyer, Th. Strunskus, F.Tuczek Langmuir 2013, 29, 8534
[7] H. Naggert, A. Bannwarth, S. Chemnitz, Th. v. Hofe, E. Quandt, F.Tuczek Dalton Trans. 2011, 40, 6364
[8] T. G. Gopakumar, F. Matino, H. Naggert, A. Bannwarth, F. Tuczek, R. Berndt Angew. Chem. Int. Ed. 2012, 51, 6262
[9] T.G. Gopakumar, F.Matino, H. Naggert, A. Bannwarth, F. Tuczek, R. Berndt Angew. Chem. Int. Ed. 2013, 52, 3796
[10] T.G.Gopakumar, M.Bernien, H.Naggert, R.Berndt, W.Kuch, F. Tuczek Chemistry Europ. J. 2013, accepted.
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11:30
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M. Dommaschk
A06
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progress report
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show abstract
MRI is an important tool in diagnostic medicine. It is gaining importance because it is working without ionizing radiation unlike Computer Tomography (CT). Contrast agents are administered to enhance anatomical details such as blood vessels. Once injected the contrast cannot be modified anymore. We are investigating nickel(II)porphyrins that can be switched between the dia- and paramagnetic state by irradiation with light. It is the first time that molecules can be reversibly switched between an MRI-active and MRI-silent state under ambient conditions.
Nickel(II)porphyrins exist in two different spin states. Square planar complexes always give rise to the diamagnetic low-spin configuration. Axial coordination of one ligand leads to a square pyramidal geometry which has a high-spin configuration. This process was coined Coordination-Induced-Spin-State-Switch (CISSS) [1].
Photoswitchable ligands can be utilized to control the magnetic state [2,3]. Azopyridins proved to be suitable for this purpose. To avoid irreversible dissociation, which would prevent application in MRI, the azopyridine was linked covalently to the nickel(II)porphyrin. The molecule is designed for exclusive coordination in cis- configuration which is the MRI-active species. The trans-Isomer cannot coordinate intramolecular. Therefore it is diamagnetic and MRI-silent [4].
The amount of paramagnetic molecules can be switched from < 5 % to 95 % with a half-life of cis-configuration of 400 days at room temperature (DMSO). For all medical applications the intramolecular LD-CISSS has to be performed in aqueous solution which is the current challenge.
[1] S. Thies, C. Bornhold, F. Köhler, F. D. Sönnichsen, C. Näther, R. Herges, F. Tuczek, Chem. Eur. J. 2010, 16, 10074.
[2] S. Thies, H. Sell, C. Schütt, C. Bornhold, C. Näther, F. Tuczek, R. Herges, J. Am. Chem. Soc. 2011, 133, 16243.
[3] S. Thies, H. Sell, C. Bornholdt, C. Schütt, F. Köhler, F. Tuczek, R. Herges, Chem. Eur. J. 2012, 18, 16358.
[4] S. Venkataramani, U. Jana, M. Dommaschk, F. D. Sönnichsen, F. Tuczek, R. Herges, Science 2011, 331, 445.
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11:50
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V. Schneider, M. K. Hedayati
C01
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progress report
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show abstract
Part I: Switching of electrical properties
V. Schneider, S. W. Basuki, T. Strunskus, M. Elbahri, F. Faupel
In this work, the photoswitching properties of composites consisting of PMMA, carbon-nanotubes and azobenzene based chromophores were investigated in a self made electro-optical measuring station. The changes in electrical resistance by illumination with ultraviolet (350 nm) and blue light (480 nm) were measured under ambient conditions. In composites containing multi wall carbon nanotubes (MWCNT) switching amplitudes of several percent were achieved, while single wall carbon nanotubes (SWCNT) showed changes up to 30 percent in resistance. Additionally the I(V) curves are quite different and the switching directions under ultraviolet and visible light illumination for MWCNT and SWCNT are directly opposite This indicates two different mechanisms to be involved in these systems. Although small thermal drifts are typically present, these systems show stable switching amplitudes which do not decay upon repeated switching.
Part II: Optical analysis of photoswitchable perfect absorber
M. K. Hedayati, A.U. Zillohu, T. Strunskus, F. Faupel, M. Elbahri
Absorption loss is generally obviated as an obstacle against the improvement of Metamaterial's (MM) performance. Recently, however, it has received wide-spread attention once its potential for hosts of application was recognized. Since the first experimental results on the fabrication of a perfect MM absorber, different strategies have been proposed and implemented to realize perfect absorber composites at different frequencies ranging from GHz to visible. Here we show the first photoswitchable metamaterial acting as perfect absorber at visible frequencies whereas its resonance peak could be broadened upon illumination by ultraviolet light. The structure is basically composed of an optically thick metal film covered by a thin polymer-spirophenanthrooxazine composite film. The as-deposited film has a high absorption band in the UV to green part of the spectrum while the band-width and intensity can be enhanced by UV irradiation. Ellipsometer analysis of the film proved that the tunability of the optical properties originated from the dispersive and dynamic nature of its dielectric function. Moreover, the optical properties of the current absorber were analyzed in comparison with the formerly demonstrated plasmonic perfect absorber.
References:
[1] M. K. Hedayati, M. Javaherirahim, B. Mozooni, R. Abdelaziz, A. Tavassolizadeh, V. S. K. Chakravadhanula, V. Zaporojtchenko, T. Strunkus, F. Faupel, M. Elbahri, Advanced Materials 2011, 23, 5410.
[2] M. Hedayati, F. Faupel, M. Elbahri, Applied Physics A 2012, 109, 769.
[3] M. Jamali, M. K. Hedayati, B. Mozooni, M. Javaherirahim, R. Abdelaziz, A. U. Zillohu, M. Elbahri, Advanced Materials 2011, 23, 4243.
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12:10
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H. Kobarg, A. Müller
C11
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progress report
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show abstract
Switching Antifreeze Activity by Light
Many organisms, e.g. fish, funghi, bacteria, plants, and insects that live in subzero regions produce antifreeze proteins (AFP) to protect them against death by freezing. To get a deeper insight into their protective mechanisms our goal is to switch their activity by light, creating a molecule that can be photo-activated with spatial and temporal resolution. Therefore tailor-made organic photochromic linker molecules based on glycoazobenzene are being synthesized and “clicked” to the AFP (Figure 1). Different carbohydrate derivatives have been synthesized and will now be used for the optimization of the coupling conditions. Furthermore, the synthesis of an orthogonally bi-functionalized glycoazobenzene is presented, which enables the coupling of the linker molecule to the peptide using two orthogonal ligation methods. On the protein side of this project, the optimization of different reactions of maleimides, haloacetamides and benzylhalides for crosslinking with cysteine residues of shortened model antifreeze proteins are presented. These now lead to the first successful cyclization of a full length type I AFP with an azobenzene linker.
Figure 1. Tailor-made photosensitive linker molecules can be “clicked” onto AFPs to allow photoswitching of antifreeze activity.
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12:30
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lunch
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14:00
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F. Temps, B. Hartke
A01
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progress report
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show abstract
Femtosecond time-resolved spectroscopy provides important information on the mechanisms and dynamics of ultrafast light-driven chemical transformations of photochromic molecular switches. Recent experimental work in project A1 has focused on (i) the effect of intramolecular electronic interactions on the dynamics of the bis- and tris-azobenzenes BPAPA and TPAPA, (ii) on time-resolved measurements of porphyrin derivatives including the "record player" molecule, and (iii) in collaboration with A. Sobolewski (Warsaw) on the dynamics of switching processes based on excited-state intramolecular proton transfer (ESIPT) and excited-state intramolecular H-atom transfer (ESIHT).
Theoretical simulations have addressed chromophore coupling in the BPAPA/TPAPA model system and have explored switching in the "record player". Employing QM/MM methods, they have also uncovered the precise mechanisms of solvent influence on photochemical switching of diazocine, establishing the first qualitatively correct quantum-yield calculation. The same QM/MM-approach has also been used to simulate the photodynamical action of a complete cilium (TATA-AB-tail) and is currently used to address the photochemistry of AB-derivatives in polymers. Completely force-field-based treatments of photodynamics are developed, in order to address even larger systems on longer time scales.
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14:20
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F. Temps, G. Friedrichs
B08
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progress report
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show abstract
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14:40
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R. Herges, O. Magnussen
B02
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progress report
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show abstract
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15:00
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R. Herges, O. Magnussen
B09
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progress report
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show abstract
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15:20
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coffee break
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15:40
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R. Berndt
B06
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progress report
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show abstract
Einzelne molekulare Schalter auf Einkristalloberflächen im Ultrahochvakuum werden mit der Spitze eines Tunnelmikroskops (STM) oder Kraftmikroskops (AFM) bei tiefen Temperaturen kontaktiert, um Schaltprozesse hinsichtlich Änderungen von Geometrie und elektronischen Eigenschaften einschließlich der Fluoreszenz zu untersuchen. Gleichzeitig werden mit einem Kraftmikroskop (AFM) die Wechselwirkungen zwischen Molekül und Spitze gemessen. Die Messungen sollen teils mit detailliert charakterisierten Spitzen durchgeführt werden.
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16:00
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R. Berndt
B07
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progress report
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show abstract
In diesem Teilprojekt sollen magnetische Eigenschaften auf Oberflächen adsorbierter Moleküle untersucht und geschaltet werden. Dazu soll vorwiegend (spinpolarisierte) Rastertunnelmikro- und spektroskopie bei T=7 K im Ultrahochvakuum eingesetzt werden. Stimuli für das Schalten sollen sein: hohe (spinpolarisierte) Ströme, die Wechselwirkung mit magnetischen Strukturen, die Einstrahlung von Licht geeigneter Energie, und Kräfte, die STM-Spitzen auf die Moleküle ausüben. Wir erhoffen uns Einsichten in die magnetischen Eigenschaften adsorbierter Moleküle, die Injektion von und die Wechselwirkung mit spinpolarisierten Strömen und Licht. Angestrebt ist, ein gewisses Maß von Kontrolle über die Spinzustände der Moleküle zu erlangen.
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16:20
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N.N.
MGK
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progress report
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show abstract
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16:40
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L. Kampschulte
Ö
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progress report
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show abstract
An overview of different outreach activities, e.g. talks, science exhibition, podcasts and the student lab klick!, which were already realised, will be given. Also upcoming events and collaborations within the SFB will be presented and can be discussed.
Literature:
Parchmann, I., Schwarzer S., Dierks, P., Könneker, K., Retzbach, J., (2013). Wie klein ist ein Atom? Größenvorstellungen als Grundlage naturwissenschaftlicher Betrachtungen. (How small is an atom? Size perception as the basis of scientific considerations.) Naturwissenschaft im Unterricht Chemie, 24 (134), 32-33.
Baum, M. & Schwarzer, S. (2013). Wie dünn ist eine Seifenblase? Ein experimenteller Zugang zu Mikro- und Nanoschichten. (How thick is a soap-bubble? An experimental access to micro-and nano-layers.) Chemie konkret (CHEMKON; Forum für Unterricht und Didaktik), 20(1), 25-28.
Blonder, R., Parchmann, I., Akaygun, S., & Albe, V. (2013). NanoEducation: Zooming into Teacher Professional Development Programs in Nanotechnology in Four European Countries. In C. Bruguière, A. Tiberghien, & P. Clément (Eds.), ESERA 2011 Selected Contributions. Topics and trends in current science education. (Accepted for publication).
Spektrum neo Heft Nr. 3 (2012). Expedition in die Nano-Welt (Expedition into the nano world)
- Schwarzer, S., Rudnik, J., Parchmann, I., Chemische Schalter als potenzielle Lernschalter – Fachdidaktische Begleitung eines Sonderforschungsbereichs (Chemical switches as potential learning switches - Subject matter education of of a Collaborative Research Center), Chemie konkret (CHEMKON; Forum für Unterricht und Didaktik), angenommen.
- Rudnik, J., Naggert, H., Schwarzer, S., Parchmann, I., Tuczek, F., „Künstliches Blut “ – Synthese eines magnetisch und farblich schaltbaren Eisen-Komplexes („Artificial (fake) blood“ – Synthesis of a magnetic and colourful switchable iron(II)-complex), Chemie konkret (CHEMKON; Forum für Unterricht und Didaktik), in Vorbereitung.
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17:00
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coffee break
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17:20
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V. Chandrasekaran, L. Kadem
B11
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progress report
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show abstract
Tailor-made surfaces and molecules to switch cell adhesion
Cell adhesion is a highly important process, both for adhesion-controlled processes in mammals, but also for medically relevant bacterial infections. Therefore, the investigation of carbohydrate-protein interaction using glycoarrays is of growing interest. Glycoarrays are carbohydrates functionalized surfaces in which carbohydrate are immobilized on different surfaces like gold, glass or polystyrene [1-2]. One of the most reliable constructions of well-ordered glycoarrays are self-assembled monolayers (SAMs) on gold. To deepen our understanding the effect of conformational changes in carbohydrate-protein interactions occurring on the glycosylated cell surfaces, photoswitchable glyco-SAMs were designed and synthesized [3-4]. SAMs which are functionalized with carbohydrate head groups and photoswitchable moiety like azobenzene, are called photoswitchable glyco-SAMs. E→Z isomerization of photoswitchable glyco-SAMs vary the presentation of carbohydrate ligands and their conformational availability to their binding partner. Photoisomerization of glyco-SAMs on the gold surface were monitored by infrared reflection absorption spectroscopy (IRRAS) and UV-Vis spectroscopy. Type 1 fimbriated bacterial adhesion of E. coli to this photoswitchable surface is currently in progress.
We have recently established block-copolymer-micelle lithography (BCML), in order to investigate cell adhesion as a function of azobenzene density. Furthermore, we recently applied block-copolymer micelle lithography BCML to a structured microtopography. Regular microtopographies on silicon wafers were obtained with photolithography followed by a wet etching process. Using these microtopographies as substrates for BCML, we were able to fabricate rectangular areas with different spacings of nanodots on one single substrate in a single spin coating step [5]. In order to enable photoswitching of mammalian cell adhesion, we have generated different surface passivation systems, different functional azobenzene units and even coupled c(RGDfK) peptides to azobenzenes and to push-pull substituted azobenzene systems. The functionality of these surfaces for cell adhesion was investigated using cell culture studies. We have also carried out single-cell force spectroscopy experiments to check the photoswitching ability of the surfaces.
[1] C. Grabosch, M. Kind, Y. Gies, F. Schweighöfer, A. Terfort, T. K. Lindhorst Org. Biomol. Chem. 2013, 11, 4006-4015
[2] J. W. Wehner, M. J. Weissenborn, M. Hartmann, C. J. Gray, R. Šardzík, C. E. Eyers, S. L. Flitsch, T. K. Lindhorst Org. Biomol. Chem. 2012, 10, 8919-8926.
[3] O. Srinivas, N. Mitra, A. Surolia, N. Jayaraman Glycobiology, 2005, 15, 861-873.
[4] V. Chandrasekaran, K. Kolbe, F. Beiroth, T. K. Lindhorst Beilstein J. Org. Chem. 2013, 9, 223-233.
[5] L. Kadem, C. Lamprecht, C. Selhuber-Unkel, in preparation.
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17:40
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A. U. Zillohu, I. Krasnov
C09
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progress report
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show abstract
Part I: Analysis of optical properties of a photo-switchable system as affected by its morphology
A.U. Zillohu, M. K. Hedayati, M. Javaherirahim, T. Strunskus, M. Elbahri
Spirooxazine (SPO) like many other photochromic compounds can be switched repeatedly between its ring opened and closed form by respective exposure to UV and visible light. The opening of the ring not only brings about the shape change (with potential application as actuator) in the molecules but also creation of a dipole which has interesting optical applications. Here, we make a comparative study of the effect of the morphology of a photochromic-plasmonic system with regard to its optical applications. PVDF and PS, loaded with SPO, were prepared in spincoated thin films and electrospun nanofibers, both as standalone systems and deposited on thin gold film as well. It was found that when the system is in the form of a film deposited on gold its transmission increases upon UV exposure. This is because of generation of dipole on the SPO ring open form which enhances the conditions for an evanescent field [1]. On the other hand applications of fibers result in a decrease in transmission because of their high scattering effect. Interestingly, the situation reverses when the film and fiber systems are studied in absence of the gold film. Now upon exposure to UV light the fibers show an increase in light transmission in a specific wavelength range. The film on the contrary shows a decrease in transmission in the same wavelength range. This study demonstrates the importance of understanding the influence of morphology for the design of optical switchable devices.
[1] M. Jamali, M. K. Hedayati, B. Mozooni, M. Javaherirahim, R. Abdelaziz, A. U. Zillohu, M. Elbahri, Photoresponsive Transparent Conductive Metal with a Photobleaching Nose, Advanced Materials 2011, 23, 4243-4247.
Part II: Micro-structural characterization of nano fibers modified with chromophores by in situ X-ray diffraction and UV-VIS spectroscopy.
Igor Krasnov, Carina Birkholz, Anja Glisovic, Christina Krywka, Nicolai Krekiehn, Ulrich Jung, Usman Zillohu, Thomas Strunskus, Mady Elbahri, Olaf Magnussen, Martin Müller
Spirooxazines and azobenzene are optically switchable molecules which can reversibly and repeatedly be toggled between a trans and a cis conformation. Associated with the switching is a change of length and dipole momentum of the molecules which might be utilized in optically excitable actuators. In order to investigate the feasibility of this idea polyvinylidene diuoride (PVDF) was blended with spirooxazine molecules and electro-spun to obtain optically active fibers in the micrometer range. Additionally, silk fibers were modified with azobenzene molecules to explore an alternative material combination and manufacturing pathway. To test the opto-mechanical properties of the modified fibers and the structural changes they undergo upon optically induced switching single fiber X-ray diffraction with a micron-sized synchrotron radiation beam was combined in situ with optical switching as well as with mechanical testing and monitoring. Additionally, the switching behavior of the fibers was studied in terms of UV-VIS spectroscopy. First results on the applicability of the combination of these techniques will be presented as well as a survey of the structural and mechanical responses of the modified silk and PVDF fibers under several photo-illumination regimes.
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18:00
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final discussion
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- publications
- miscellaneous
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18:45
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dinner
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